Why the translation inconsistencies?

That's interesting. When Gaspard Ulliel was yelling "Manech aime Matilde" it sounded to me like he was saying "Manech et Matilde" so I didn't understand what the initials were originally supposed to mean. I think they shouldn't have changed that, though it does contribute a little more to the depressingness when Manech keeps carving MMM everywhere if it means "Manech is marrying Mathilde" as that seems more and more impossible.

This makes me wonder exactly at what point they became engaged. Benedicte appears to be surprised when he kisses her goodbye, as if she didn't know yet they'd become lovers.

"Ah, you've come to read my trousers!"

Wow, you people sure are intolerant when it comes to the poor translators!
First of all, some things are just not properly translatable. Second of all, translation is not about just giving a literal translation of a text. It's about conveying the entire meaning. I've been to translation school, and this is what they teach you there. I find it a bit harsh that so many of you say that it is "stupid" to translate the MMM as "Manech's marrying Mathilde". The translators were stuck translating MMM, which is important to the plot, as one wounded soldier mentions M's and the german soldier's sister leaves 3 M's on the chalkboard. So what were the translators to do? "M. aime M", i.e. "Manech aime Mathilde", is pronounced M-M-M in French, so in the original film it makes sense (or course). But anything like "Manech loves Mathilde" makes MLM, which won't do because on the screen we see MMM (repeatedly). So the translators are stuck with figuring out something for MMM. Okay, granted "marrying" isn't the greatest choice, but what would have been better? I defy all of your geniuses to come up with a better word. Sorry, it's not a perfect world. Be happy that you have the English translation, which has something like "I am the squid's servant" when the children are playing, instead of the Dutch version which simply skips over these lines. If the translation had read "Manech loves Mathilde" someone would be here posting that it doesn't makes sense with the MMM.
One of the greatest movies ever made!

Poor things, you're all complaining about English subtitles trying to keep the acronym MMM instead of making a literal translation.
You think you had it all bad?
The Spanish subtitles for this movie (when I watch movies in English, I use English subtitles but I rarely see them, when I watch movies in Latin-based languages like Italian, French or Portuguese, I use Spanish subtitles) read "Mannech aMa a Matilde"... with the upper case M and everything.
Now, THAT's an awful way to keep an acronym, not yours. Pity us!

It's so cliche to put Spoiler tags on your signature