So here's some info about languages in this game. The NTSC version only has English but the PAL version has six languages: English, French, German, Spanish, Italian and Dutch. Out of all the languages that aren't English, Spanish and Dutch seem to be the fastest from the small amount of testing I've done. Either language can be faster in boss ILs depending on the boss (Dutchman is fastest in Spanish for example). As for full game runs, it can't be said if any language is faster than English yet as there's a lot more text to examine and nobody has looked into it yet. If anyone is willing to do in depth testing to time each language, that would be highly appreciated and then I can edit this thread with extra info.
I'm glad to see someone else is looking into this as well - I've been suspecting that some languages are significantly faster than others for a while, I just haven't found the time and motivation to do some real research yet. So here's a method I've come up with that should tell us pretty precisely which language is the fastest (for a full game run). Step 1 is recording a full run of the game, letting all texts appear in their natural speed (so no fast forwarding by pressing or holding A). Step 2 is taking that recording and feeding it into a decent video editing software and cutting out everything before and after the texts, so that, in the end, a video of just the texts remains. This should tell us the exact time that each language takes. Of course the cutting has to be executed precisely and consistently to get a good result. I am aware that this would be a tedious process to do for every language, so if any of you guys has a simpler method, please share!
EDIT: On second thought, if done right, the whole natural speed thing isn't actually necessary.
Small update: So far, I have recorded a playthrough in each language and will start timing them soon. I have made an interesting discovery already though: There is one cutscene missing in the non-English versions (the one before entering 5-1). I've actually fired up my Gameboy Advance to double check this. No idea why they've removed it, but it does make the English version a few seconds slower.
The results are in! Spanish is indeed the fastest language for the full run and also most bosses. Only the two Dennis bossfights are faster in other languages. You can find all the details in this document: https://drive.google.com/open?id=19KTv5ZaWyJqxyVR44wcezNWs4HRh6Okg Have fun!
