Great progress! Some suggestions:
CARKEYS > CAR KEYS
AN EURO > A EURO
THE DIRECTORS AGENDA > THE DIRECTOR'S AGENDA
A NOTE OF A POISON JAR > RECEIPT OF A POISON JAR
A TAPE BAND > A CASSETTE TAPE
AN REVOLVER > A REVOLVER
THE COMBINATION OF A COMBINATION LOCK > THE COMBINATION LOCK CODE
ELTON JOHNS > ELTON JOHN'S
FURTHER MORE > FURTHERMORE
Furthermore the capitalization details were lost in this text document, not sure if it can be added back easily as there are also capitals mid-sentence (e.g. personal names).
As I already commented I don't think all strings will fit. Replacing foundation with founding just doesn't sound right and probably there will be others. Perhaps these can be cut off in the programmatic process and then manually corrected - that's doable as long as the number of strings to be corrected stays low.
What does ("S"=D3h) mean behind SOME KIND OF FORM. ? Do I need to do something with this or is it a remark for yourself ?
It just a remark for the first character because the bit 7 must be set. Do not take this into account.
@Hrotgar: Thanx for your suggestion, I've updated the txt file. I will try too keep the textlenghts in mind, and will put comments where a problem arises (like with foundation aka founding).
I couldn't resist, here are the corrected lengths. I have commented with <-- where suggestions are welcome.
correcte sentence lengths
Does the translated text length have to be <= original Dutch text length, or is there some room to play with (here & there)?
@ren: If the english text is smaller that's okay, larger is the problem. That's why I had to walk through all translated texts again to make sure the length is the same or less.
Ok, I have some suggestions, will post some later.. 
Ok, I've gone through line 1 to 100, and made some improvements (debatable) and corrections.
If you like this, I can do some more tomorrow 
Btw: I did finish this game, and know some contexts (that helps of course ), though can't remember everything exactly. (Though I could check Vampier's speed run on YT of course.. )
{edit: but perhaps I'm doing double work: John has been busy editing already. Or are these already integrated? Status update prease :))
Here are some suggestions, also think about if you want this in US or UK English.
For instance, CHEQUE is UK English, while CHECK is US English.
Here are some suggestions. Note I did not pay too much attention to line length.
EEN HUISSLEUTEL - A LATCHKEY A HOUSE KEY EEN CHEQUE OP UW NAAM - A CHEQUE ON YOUR NAME A CHEQUE IN YOUR NAME UW TOEGANGSKAARTJE - YOUR TICKET YOUR ADMISSION TICKET EEN NOTA VAN EEN POT GIF (BEWIJS!) - RECEIPT OF A POISON JAR (EVIDENCE!) RECEIPT OF A JAR OF POISON (EVIDENCE!) EEN SCHERPE SCHAAR - CUTTING SCISSORS SHARP SCISSORS EEN OF ANDER FORMULIER. - SOMEKIND OF FORM. SOME KIND OF FORM. ZOU DIT OPEN KUNNEN? - CAN IT OPEN? COULD IT BE OPENED? HET KANTOOR VAN DE STICHTING HULP AAN EENZAME DIEREN. - THE OFFICE OF THE FOUNDATION TO AID LONE ANIMALS. THE OFFICE OF THE FOUNDATION TO AID LONELY ANIMALS. NOU AL MOE? - TIRED YET? TIRED ALREADY? ZEKER NU ER DE LAATSTE MAAND VOOR MAAR LIEFST FL 314.159,27 AAN NIEUWE DIEREN IS UITGEGEVEN. - SURELY NOW THE LAST MONTH IT ISSUED $ 314.159,27 FOR NEW PETS. ESPECIALLY SINCE IN THE LAST MONTH $ 314,159.27 HAS BEEN SPEND ON NEW ANIMALS. VERDER BLIJKT DAT DE GESTORVEN EXEMPLAREN GROTE HOEVEELHEDEN LANDBOUWGIF IN ZICH HADDEN... - FURTHERMORE THE DEAD SPECIMENS SEEM TO HAVE LARGE QUANTITIES OF PESTICIDES IN THEM... FURTHERMORE IT APPEARED THE DEAD SPECIMENS HAD LARGE QUANTITIES OF PESTICIDES IN THEM... IN EEN VAN DEZE LADES MOET TOCH HET ARRESTATIEBEVEL LIGGEN! - IN ANY OF THESE DRAWERS THE ARREST WARRANT MUST BE! IN ONE OF THESE DRAWERS THERE MUST BE AN ARREST WARRANT! IK VIND DAT U ER ONBETROUWBAAR UITZIET, MAAR DE CHEQUE WORDT TOCH GEACCEPTEERD, ALSTUBLIEFT TIEN GULDEN. - YOU SEEM UNRELIABLE, BUT THE CHEQUE IS STILL ACCEPTED, PLEASE TEN EUROS I FIND YOU APPEAR UNRELIABLE, BUT YOU CHEQUE WILL BE ACCEPTED, HERE IS 10 EUROS LOKET 2 IS WEGENS ZIEKTE GESLOTEN. - DESK 2 IS CLOSED DUE TO ILLNESS. COUNTER 2 IS CLOSED DUE TO ILLNESS. HIER WORDT NET KOFFIE GEDRONKEN. - JUST DRINKING COFFEE HERE. COFFEE IS BEING DRUNK HERE. DE MAN ACHTER DE KASSA KIJKT U NORS AAN. - THE MAN BEHIND THE CASH DESK LOOKS SOUR. THE MAN BEHIND THE CASH REGISTER LOOKS SOUR AT YOU. DE GARAGE IS TE VIES OM ZO AAN TE PAKKEN... - THE GARAGE IS DIRTY BEYOND BELIEVE... THE GARAGE IS TOO DIRTY TO HANDLE... IN DEZE BOEKENKAST ZIT VAST IETS VERSTOPT! - THIS BOOKCASE HIDES SOMETHING! THERE IS CERTAINLY SOMETHING HIDDEN IN THIS BOOKCASE! HET KANTOORTJE VAN J.GREIN, DE MAN ACHTER DE KASSA. - THE OFFICE OF J.GREIN,THE MAN BEHIND THE CASH DESK. THE OFFICE OF J.GREIN,THE MAN BEHIND THE CASH REGISTER. DE TEKSTEN ZIJN DOOR DE ZON VERBLEEKT. - THE TEXTS BEEN TAINTED BY THE SUN. THE TEXTS HAVE BEEN BLEACHED BY THE SUN. DE BEWAKER VERTELD: "DE LAATSTE TIJD STERVEN ER STEEDS DIEREN. ZE ZIJN HOPELOOS! - THE GUARD STATES: "LATELY ANIMALS ARE DYING. THEY ARE HOPELESS! THE GUARD STATES: "LATELY ANIMALS ARE DYING INCREASINGLY. THEY ARE HOPELESS! HET ZOU NATUURLIJK RAMPZALIG ZIJN VOOR ONZE REPUTATIE ALS DIT BEKEND WERD. - IT WOULD BE DISASTROUS FOR OUR REPUTATION WHEN THIS CAME OUT. IT WOULD OBVIOUSLY BE DISASTROUS FOR OUR REPUTATION IF THIS CAME OUT. VANDAAR DAT WE IN HET GEHEIM NIEUWE DIEREN KOPEN. - THAT IS WHY WE SECRETLY BUY ANIMALS. THAT IS WHY WE SECRETLY BUY NEW ANIMALS. DAT AL HET PERSONEEL IN VERBAND MET BEZUINIGINGEN EEN LOONSVERLAGING TE WACHTEN STAAT. - DUE TOO THE RETRENCHMENT ALL PERSONNEL WILL BE CUT ON SALARIES. DUE TO CUT BACKS ALL PERSONNEL WILL RECEIVE REDUCTIONS ON THEIR SALARIES. HIJ HET VOER DAT ELKE OCHTEND STIPT TE LAAT GEGEVEN WORDT NIET MEER VERTROUWT. - HE DOES NOT TRUST THE NOURISHMENT GIVEN TO HIM EVERY MORNING PROMPTLY LATE. HE DOES NOT TRUST THE FOOD GIVEN TO HIM EVERY MORNING ROUTINELY LATE. TWEE GEMOEDELIJKE DIKHUIDEN STAAN TE MEDITEREN. - TWO EASY-GOING PACHYDERMS ARE MEDITATING. TWO EASY-GOING ELEPHANTS ARE MEDITATING. U KIJKT OP UW GEMAK DE KOOI ROND EN VINDT EEN ZEER BELANGRIJK BEWIJSSTUK! - YOU LOOK AROUND THE CAGE AT YOUR EASE AND FIND A VERY IMPORTANT EXHIBIT! YOU LOOK AROUND THE CAGE AT YOUR EASE AND FIND A VERY IMPORTANT PIECE OF EVIDENCE. DE LEEUW BEDENKT ZICH GEEN MOMENT EN VLIEGT U NAAR DE KEEL. - THE LION DOES NOT HESITATE AND FLIES TO YOUR THROAT. THE LION DOES NOT HESITATE A MOMENT AND JUMPS AT YOUR THROAT. EEN GROEPJE LEVENDE OVERSTEEKPLAATSEN EN EEN DRONKAARD. - A SMALL GROUP OF LIVING CROSSINGS AND A SOT. A SMALL GROUP OF LIVING CROSSINGS AND A DRUNKEN SOT. DE DRONKAARD KIJKT U WAT PIPS AAN EN ZEGT "HEB JE WAT TE DRINKEN, ZE HEBBEN DIE BAR DEFINITIEF GESLOTEN... - THE SOT LOOKS AT YOU PALELY AND SAYS DO YOU HAVE SOMETHING TO DRINK,THEY CLOSED THAT BAR PERMANENTLY... THE DRUNKEN SOT LOOKS AT YOU PALELY AND SAYS DO YOU HAVE SOMETHING TO DRINK,THEY CLOSED THAT BAR PERMANENTLY... DE ZEBRA NEEMT HET U HOOGST KWALIJK DAT HIJ TIJDENS ZIJN GRAS-DESSERT GESTOORD WORDT EN GEEFT EEN FERME TRAP MET LINKS-ACHTER. - THE ZEBRA BLAMES YOU FOR INTERRUPT HIM DURING HIS GRASS DESSERT AND GIVES YOU A STURDY KICK WITH LEFT BEHIND. THE ZEBRA BLAMES YOU FOR INTERRUPT HIM DURING HIS GRASS DESSERT AND GIVES YOU A STURDY KICK WITH HIS LEFT BEHIND. PER ONGELUK RAAKT HIJ UW HOOFD. WE PLEITEN DAN OOK VOOR DOODSLAG... - BY ACCIDENT HE HITS YOUR HEAD. WE PLEAD HOMICIDE ... BY ACCIDENT HE HITS YOUR HEAD. WE THEREFORE PLEAD HOMICIDE ... KIJK MAMA EENS DANSEN! - WATCH MAMA DANCE! WATCH MOMMY DANCE! (If US English) OM AL HET WATER OP TE DRINKEN VERDRINKT U... - TO DRINK ALL WATER YOU DROWN... TO DRINK ALL THE WATER, YOU DROWN... EEN REUSACHTIG MODEL VAN EEN TYRANOSAURUS. - A HUGE MODEL OF A TYRANOSAURUS. A GIGANTIC MODEL OF A TYRANNOSAURUS. EEN ZWAKKE SCHAKEL IN DE CONSTRUCTIE BEGEEFT HET EN HET GIGANTISCHE MODEL BEGINT TE VALLEN. - A WEAK LINK IN THE CONSTRUCTION FAILS AND THE GIANT MODEL STARTS TO FALL. A WEAK LINK IN THE CONSTRUCTION FAILS AND THE GIGANTIC MODEL STARTS TO FALL. EEN PARKIET DIE MISSCHIEN WEL KAN PRATEN... - A PARAKEET THAT MIGHT TALK... A PARAKEET THAT MAY BE ABLE TO TALK... VOEREN IS TOEGESTAAN. - FEEDING ALLOWED FEEDING IS ALLOWED EN IS NU BLIJ DE TRALIES EENS VAN DE ANDERE KANT TE KUNNEN BEKIJKEN. GELUKKIG HOEFT DIT NIET 25 JAAR, DE RECHTER DIE HET VONNIS VELT BLIJKT NAMELIJK IN ZIJN - AND IS GLAD TOO SEE THE OTHER SIDE OF THE BARS. LUCKELY IT DOES NOT HAVE TO BE 25 YEARS SINCE THE JUDGE APPEARS AND IS GLAD TOO SEE THE OTHER SIDE OF THE BARS. LUCKILY IT DOES NOT HAVE TO BE 25 YEARS SINCE THE JUDGE THAT GIVES THE JUDGMENT APPEARS JEUGD DOOR EEN HOND GEBETEN TE ZIJN WAT ZICH NU MANIFESTEERD IN EEN LEVENSGROTE DIERENHAAT. LEUK VOOR JACK, WANT DIE WORDT NU VEROORDEELD TOT 1 MAAND - TO HAVE BEEN BITTEN IN HIS YOUTH WHICH MANIFESTED IN A LARGE ANIMAL HATE. NICE FOR JACK, BECAUSE HE IS SENTENCED TO 1 MONTH TO HAVE BEEN BITTEN BY A DOG IN HIS YOUTH WHICH MANIFESTED IN A LARGE ANIMAL HATE. NICE FOR JACK, BECAUSE HE IS SENTENCED TO 1 MONTH GEVANGENISSTRAF EN HET VERPLICHT SPELEN VAN ICONVENTURES VAN RADARSOFT. - IMPRISONMENT AND COMPULSORY PLAYING ICONVENTURES OF RADARSOFT. IMPRISONMENT AND COMPULSORY PLAYING OF ICONVENTURES FROM RADARSOFT. ...EN PROBEER HET DAN NOG EENS! - ... AND TRY AGAIN! ...AND THEN TRY AGAIN! CENTREER HET BEELD VOOR U BEGINT. - CENTER SCREEN BEFORE YOU START. CENTER THE SCREEN BEFORE YOU START. (US English) CENTRE THE SCREEN BEFORE YOU START. (UK English) U ZIT ER NAAST! - U ARE OFF! Possible translations: YOU MISSED! WELKOM BIJ "ZOO", CRACKED BY È. Ò. Â. * 10-1-1988 - WELCOME AT "ZOO", TRANSLATED BY GDX AND THE KID 1-2-2017 Do you really want to leave the CRACKED BY? HIER LIGT NIETS MEER. - THERE'S NOTHING HERE. THERE'S NOTHING ELSE HERE. DE AANHOUDER WINT (SOMS), DUS RUST IN VREDE... - PERSISTENCE PAYS(AT TIMES),SO REST IN PEACE... PERSISTENCE (SOMETIMES) PAYS, SO REST IN PEACE... MAAR EEN AANTAL HEB IK ER TE PAKKEN GEHAD, VOORAL DIE GORE GORILLA DIE ME ALTIJD UITLACHTE, ROTBEEST! - BUT I TOK CARE OF SOME OF THEM, ESCPECIALLY THAT STUPID GORILLA THAT ALWAYS LAUGHED AT ME,BASTARD! BUT I GOT SOME OF THEM, ESPECIALLY THAT DISGUSTING GORILLA THAT ALWAYS LAUGHED AT ME, BASTARD! JE HEBT NIET GENOEG BEWIJS IN JE KOFFER, HUFTER! - NOT ENOUGH EVIDENCE IN YOUR SUITCASE, ASSHOLE! YOU DO NOT HAVE ENOUGH EVIDENCE IN YOUR SUITCASE, ASSHOLE! UIT VERTROUWELIJKE BRONNEN IS VERNOMEN DAT DE PLAATSELIJKE ZOO IN HET GEHEIM GROTE HOEVEELHEDEN DIEREN AANKOOPT. - CONFIDENTIAL SOURCES HAS LEARNED THAT THE LOCAL ZOO IS PURCHASING IN SECRET LARGE QUANTITIES OF ANIMALS. FROM CONFIDENTIAL SOURCES IT WAS LEARNED THAT THE LOCAL ZOO IS PURCHASING IN SECRET LARGE QUANTITIES OF ANIMALS. ALS MEDEWERKER VAN DE DIEREN-HULP-ORGANISATIE IS HET UW TAAK UIT TE ZOEKEN OF HIER EEN MISDAAD IN HET SPEL IS. - AS AN EMPLOYEE OF THE ANIMAL HELP ORGANIZATION IT IS YOUR JOB TO EXAMINE IF A CRIME IS COMING INTO PLAY. <-- IF A CRIME IS COMING INTO PLAY -- SUGGESTIONS WELCOME --> AS A MEMBER OF THE ANIMAL RIGHTS ORGANIZATION, IT IS YOUR JOB TO EXAMINE IF A CRIME IS BEING COMMITTED. HEEFT U EEN SCHULDIGE GEVONDEN DAN BENT U GEMACHTIGD HEM OF HAAR TE ARRESTEREN. - WHEN YOU HAVE FOUND SOMEONE GUILTY YOU ARE AUTHORIZED TO ARREST HIM OR HER. WHEN YOU HAVE FOUND A GUILTY PARTY, YOU ARE AUTHORISED TO ARREST HIM OR HER. U KUNT DINGEN OPENEN OF BEWEGEN DOOR HET JUISTE VOORWERP OP TE PAKKEN EN HIERMEE EEN BEPAALD IETS OP HET PLAATJE AAN TE WIJZEN. - YOU CAN OPEN OR MOVE THINGS BY POINTING THE RIGHT OBJECT AT THE RIGHT SPOT. YOU CAN OPEN OR MOVE OBJECTS BY PICKING UP THE RIGHT OBJECT AND POINTING WITH IT AT THE PICTURE. SUCCES, EN.... PAS OP! - GODSPEED, WATCH IT! GODSPEED, AND... WATCH IT!