My native language is french, yet I like to think myself as fluent in english (even if my written english must be scattered with faults) and blabering in german ^^
I use Google translate to get specific words I don't know/get (either french to english, or the opposite and eventualy other languages from time to time). The fact that it displays different words and synonymous help understanding.
But having complete sentences translated through google translate is a no go. No actual translator is accurate enough atm to make the link between what is meant and what is said. So most of the time litteral translation has no meaning.
Moreover most french people on the internet can't even write proper french nowadays. Grammar is completely off, ponctuation disapeared. Most of those young peoples (from 8 to 18/20/+) allegate that internet is no school so they can write the way they want. They don't get that the complexion of french grammar and the precision of its vocabulary helps them to express themselves.
Truth is nowadays they don't have much interesting things to express anyway.
I'll stop my rant for now and go further on the subject asked.
I've been involved in the growing of a french speaking community around an originaly english-only game. (toribash - toribash.com | http://www.toribash-fr.net)
The main forum (the one the developpers of the game put up to host/manage the global community) is strictly english.
They have been trying to develop foreign languages by allowing certain parts of the forums (a university/school of some sort named unibash) to be multi-lingual.
Also, official clans' boards (hosted on the official forum) can be held in any language, as long as the mods see regular activity, they are fine with it.
What we've been experiencing is that french dudes manage to get there way in (registering an account, even if they are under 13 yo (normaly not allowed)), go ingame and play.
Most of the time, it is chatting in the game's rooms that helps meeting other french people. Some will direct the new comer to their clan board (the first official french speaking clan of the game), others will direct to the external forum we put up (tb-fr).
For "ages" I've been asking TB staff to put some clear links in the forum index in foreign languages that links to the external forums of communities, because most of non english speakers have gathered and developped their community on their own. Russian community used to be huge, a lot of spanish/latin members also. French speaking community is not the biggest, but still we have regular turnover in new comers/ activity and a regular members basis (over the last 2 years of the french community's existence).
This model doesn't really apply to a soft like construct imo though.
On a personnal note, when I discovered construct, I have been gladly charmed by the maturity of its community.
Most of the questions asked were asked by people who trialed/errored and searched through the forum before asking it seemed to me.
I'm afraid that the more exposure you'll give to construct (though this exposure is what you (scirra) is naturaly and understandably going for) the more of "boulets" (that's the french term for idiotic ppl who can't even take the time to read the informations already posted and try to understand them before asking) will be dragged here.
That's a personnal fear and I know those people are frustrating and quite hard to manage. Because the more complex things you write them to answer their questions, the more stupid questions they will ask.
Most of them would like to know how to make a game (as they might say) but in fact the truth is they would like to imagine something in their head and that this stuff happens by magic.
I'm ranting again so I guess I'll stop by now.
To sum up on the subject. I think that french people who can't speak/understand english fluently will get their head around some parts of the forum/site though (tutorial part is easily spottable as it is now part of the internet language more than a specific idiomatic language). So for example, having translations of the existing tutorials by example could be useful.
But as having the forum translated, it is not likely to happen any time soon. As I stated earlier no language translator is that good yet.
So having ppl speaking both languages (english and whatever other language is implied) will still be the good solution.
You might wanna developp some regional parts/groups, in which people who speaks the same language will be able to gather and exchange their tips, ask for stuff and/or translations of already existing english posts in their own language.
Having clear links on the index of the site or forum might help lead newcomers to the most clear source of informations for them. (once again depending on their language).
As we know, having such a structure will depend on outside people (from scirra) managing those communities, yet refering to scirra though so that the global community goes the same way.
I maybe went further then what you expected Tom (^^) but here's my wallblock of text about what you were asking :P