That hit the spot!
To Armogohma. Well, just to get you started. Open your Notrium\textures folder and look for a file named font.png. Open it with some image viewer. See these letters and digits. Digits are ok, I presume, so look at the letters, big and small. Are they enough for a Dutch translation? If so, you could start translating right away (see details below). Otherwise, you should think it over. If given alphabet is not suitable for Dutch (or whatever language one is translating to), it is, in fact, impossible to do it in a proper way (without transliteration and all that pervert stuff ).
Now, if the alphabet suits you at the minimum at least, let's look what to do.
AFAIK, all texts in Notrium are located in the data\ folder, each data file belongs to some mod. Since you want to translate Notrium itself, you'd go to the Default\ folder there.
Generally, I'd suppose now that you read modding FAQ, because the contents of each .dat file are pretty intuitive (open them with any text editor).
If not, I'll give you some quick hints. To make a partial translation (the main menu can't be translated, we'll have to go with that) you'll need to modify only these several files:
- animation.dat - the text on those comics-style screens for intro and outro
- dialogs.dat - there aren't so many dialogs in Notrium... whatever
- items.dat - the most vast piece of work goes to items' description
- journals (journal_alien.dat, journal_android.dat, journal_human.dat, journal_psionic.dat, never mind about the journal_empty.dat, don't change it) - those annoying messages you get over time
- player_races.dat - player races comments, the ones you see when you choose your race
I hope I didn't miss anything. Good luck in any case.
P.S. If something got screwed because of some changes and you don't know what's going wrong and don't want to redo much work, use some text file comparison utility like WinDiff to see what is different from original Default mod (yeah, back it up, will'ya?)