Sorry, don't have any experience of bi- or multi-lingual guilds - but the guild I have been a part of since start of WoW has always been multinational. We came to WoW from another MMOG, though, so we were already set on using English as the modern-day Latin.

While we throw around some words in different languages, the guild chat is 99% English. Raiding is done in English because of communication, as said.

We haven't had any known deaf members of the guild, but there have been a lot of people who have had problems setting up their Teamspeak client (most of them were embarrassed about their English), some of which could have been deaf for all I know.
There has certainly been a few pulls in Molten Core where I believed no one was listening!

We've had a deaf person playing - as far as I know he(?) still plays with the guild. I can't remember it ever being an issue, but he did very thorough research on all the encounters so he never had to have much explained to him. Besides it's not exactly a language barrier - you could always just explain in tells. I'm not a native English speaker, but on a US realm I obviously spoke English.

I disagree. In my experience, some of the people with the poorest grammar I've ever met are American (no, I'm not kidding - I have many friends abroad).

People that learn English as a second language tend to be more aware of the rules that Kaubel and others (God bless them) enforce so strictly. Like, the difference between "your" and "you're" for example. Or when an apostrophe is needed vs. when it's not.

I once read a shirt that said "A man who knows only one language knows nothing of it." I couldn't agree more.

As an officer in a guild where there are players from all over Europe and even some from Middle East I must say language isn't a big issue. I have never seen a very good player with bad english. Although I have seen lots of scandinavian and dutch people having really good english and playing with poor performance.I didn't exactly pay attention but not a single player from our guild comes into my mind who is a great player but hardly can speak english. Although I can easily think of many average players.

We have a British raid leader, an American healing officer and a Turkish main tank(being me).And so far cultural differences added only variety to our guild. Sure it was not good when our old arabic players from UAE had to pray 15 minutes before raid. But those are extreme examples.If the so called guild spirit is always kept high and people do what they are supposed to do language and culture isn't a problem.

Right now we have a hunter from Romania who can hardly speak english, but understands what our hunter leader and/or raid leader says very well.He can hardly speak but he can type. And he can type fast.For a reason I find slow-reacting people more irritating then those who have a bit of problem with English.

For me it is about clear sentences and dialect.If people can prove a point without confusing other people, and If those people don't whisper to each other like "What did he just say?" it is good enough to play this game.

I use to be in a guild pre-BC where the GM and a couple of the starting officers lived in Mexico. It was clear by their accent that Spanish was their native tongue but they spoke English quite well. We were semi-casual and progressed up to Huhu in AQ40 with the majority of the members English speaking but we also had a few (5 per raid on average) that only spoke Spanish.

I don't believe our progress was hindered by this as it was a fairly casual guild to begin with but it did make pulls longer having the raid leader give two sets of instructions before and after pulls. I suppose we were lucky that the GM was VERY fluent in both languages and could translate on the spot if a class lead ever needed to talk to one of the members in the other language.

The experience required a little patience but overall I would say that it was very positive and educational as I tried to expand my Spanish beyond "Cerveza Por Favor"

did you actually just say "Singaporean" ?

Singlish! Thank you for explaining a language i've been reading in gchat for two years

Our guild was fairly successful pre BC and is finishing T5 content now, officers and leaders are 90% from Singapore, the rest are Australian with one or two randoms from places like germany, phillipines & India (I kid, I kid, we just laugh at him because he sounded indian).

gchat is mostly in english with a smattering of "Singlish" and I'm ashamed to say as an Australian that I picked up a lot of it and it became a habit to talk singlish to guildies. So bad that people would ask me "hey I thought you were from aus, are you from singapore???" Having cleared all of MC without a Vent server it was never really a barrier, once we got into bwl we did have to have things explained in malaysian (or whatever their native language was) in whispers for those that didn't understand the english explanations on vent. Language definitely wasn't a barrier there, plenty of bad players that do or don't speak english

I would like to share my own experience.

I'm argentinian, I live in Switzerland (in the French part of it) since 5 years now and ofcourse I need to speak french for in my IRL. I didn't know french when I arrived here, and I must say WoW helped me a lot in that area. Reading the guild's chats / commerce / pick up groups, listening at TeamSpeak pushed me forward to further develop my french and all my guildmates helped me as well to better interact to everyone in the game.
I've always been part of french speaking guilds and I didn't speak french when I started to play WoW (2 years and a half ago).
I have always had a MT role, so I needed to know game mechanics, encounters, etc. To the point that I actually became the "tactical writer / Raid Leader" of one of the guilds for the TBC content.

It was nice to see that many people really appreciated to have a "different" raid leading experience, as I have a very strong accent, it sounds funny. And made raiding more enjoyable. (as a side note, girls love the accent :P)

I think it will always depends on people's tolerance and willing to learn from / share with / be open to other cultures.

I play on an European server and I've been most of my WoW time in "international" guilds, with people from different countries. I started out in an all-Dutch guild, but the problem with that is that you have a very small group of people to recruit from. Other guilds on our realm have been going down because of that as well. So basically all "successful" guilds have to recruit people from different countries. I think most of the time this is not a problem, as joining such guilds requires you to post an application, and in order to do that you need to be able to speak/write decent English.
We hardly use "multiple" languages during raids or whatnot. In order to do that, people would need to speak both languages or you need to repeat everything twice. Sure, if I want to say something quick in raid to someone who is Dutch, I often say it in Dutch instead of English, but that's about it.

However, you can see some clear differences between cultures. In my former guild (also international), there were some Portuguese people that had to eat during raid time, because their dinner times are a lot later than most of Europe. (I suppose the same counts for Spanish/Italian people, but I haven't met any of those on our server yet.)

Also, we had a lot of people from Saudi Arabia. I tell you it is not fun to stand before Curator, on a respawn timer and then having to wait 20 minutes because some people have to do their daily praying. :P But not much you can do about it of course, so eventually you can learn to work around that. It's funny to see them talk Arabic, it's half 1337 5p34k, as they use numbers in their words (their alphabet has more characters than ours afaik).

I was recently in a pretty casual Karazhan guild on my old main. I really liked most of the people, but four or five people in the guild spoke excellent chinese and very, very poor english. The end result was that they would try, bless them, to communicate in english during raids, but more often than not vent would be filled with voices chattering away in chinese.

It can be frustrating, and it's the ultimate reason I left my guild. Without trying to sound xenophobic to an extreme, shit like that can polarize your guild and split it into english speakers and non english speakers. My attitude tends to be something like "if you're on an english server, please make every effort to communicate in english."

My guild which has consisted of players from Sweden, Finland, Denmark, Germany, Belgium, Holland, France, the UK, Hungary and Spain have neve had any problems when it comes to spoken language apart from three small things:
*Finnscursing at eachother.
*Finns showing off to the raid how many Swedish curses they have learned.
*The Spanish guy speaking way too fast. Since the Spanish language is a bit more fast paced than English there were times when no one could understand him, especially when he ws in a hurry or excited.

However, since my realm was the unofficial Hungarian realm, I've been in plenty multi-guild raids to Onyxia, MC and the outdoor bosses where there have been two spoken languages on Ventrilo. Since all those encounters were old news for the guilds by the time we formed those raids we never had any problems though. Assignments went around and as soon as the fight started, communication was not needed.