Here are some principles:
Create one account per language. I mute people who tweet in too many languages. Don’t abuse your audience’s attention. Now reread this principle and translate it into all the languages you know. This is one top item that ruins the twitter experience when it comes to foreign languages. Exceptions would be Swedish/English or Tagalog/English where bilingualism is the norm. But Swedish/Chinese is still stupid.
Be a poseur. Google translate exists, use it. It’s better to cheat and use google translate than to never interact with people on twitter. When you interact with people, your brain takes communication seriously. This is powerful stuff. If Google translate gets you to read and interact more, go for it. Your reading skills will improve. Your motivation will improve. Don’t hold an aesthetic disapproval of google translate hold you back.
Use google translate effectively. Fix all the errors you can find in the google translate before you post it. If you don’t get “this feels right,” then try different English until it looks right. Simplify. If you know zero of your target language, this might not work– I haven’t tried it. It works best if you know just enough of the language to have a feel for what looks right.
Follow a lot of people. Follow 500 to 1000 accounts. Turn off the retweets or a stream that large is unmanageable. Anyone tweeting 50,000 tweets over a small number of years needs to be followed & muted. They are good for interaction but will flood your feed.
Mute! Mute! Mute! If they tweet-flood: mute ‘em. If they tweet in 5 languages, mute ‘em. If they know language X (which you care about), but only tweet in Y, mute ‘em. They won’t know they have been muted, but will still be able to interact with you should they ever follow you. Think about it, the Esperantist that tweets only (or 98%) in Chinese: they want to be muted, don’t consider it rude. If you don’t want to be muted, see principle #1, one language per account.
Schedule conversation starters. Don’t schedule low quality content like proverbs, inspirational quotes and other crap. Instead tweet questions, jokes and so on. When I tweet on my professional account, there are lots of organic reasons that I want to write something. For language this or that, unless I’m traveling, I got nothing driving my chatter, so I need something else to keep things moving forward.
Don’t cross post from facebook. Invariably this leads to the content getting cut in half or worse, it’s a bare link, the lowest quality tweet possible.
Hold back on the meta. It is tedious to listen to people talk about how well they speak language X, or how many they know, or so on. Do talk about linguistic musings, funny observations, etc. Don’t tweet too much about twitter.