Tried to learn a language when overseas teaching? Were you successful? Any tips or techniques or resources that you found useful in doing so?

If so please share them here with everyone, Thanks.

Conversational Mandarin after 1.5 years in China, nearly fluent in Japanese after a few years here.
The secret i think to learning another language is to immerse yourself in it. You really need to be living amongst it and speak it every opportunity that you get. Confidence is the main factor.

I've learned a lot of languages and I've learned them in a a lot of ways as well...

In my experience, the most effective away of learning a language and retaining it is through immersion. For a lot of us though, it's not so easy to immerse yourself in another country to learn another language. In these cases, the best way I've learned is through friends teaching me and through using what I learned in practical situations as much as I can.

For example, I learned Korean informally through home stay students who have stayed in my home. I had informal lessons but I learned quickly and retained much of what I learned because I would practice what I learned often on every Korean that I met. I would use what I learned in practical situations. Until now, I haven't forgotten the things that I've learned. My learning has taken a plateau but that's b/c I haven't been looking to improve or learn more.

Sad to say, where I've learned a language and retained the least of it is in the classroom. I've taken French in class from elementary to university and I still can't speak French to save myself.

On the other hand, the most important factor in learning languages in general is motivation. If you are not motivated to learn a language, that's a big block that would impede your language learning. So another tip I would give, is to find ways to keep yourself interested in the language you are learning. Make friends who speak the language or watch dramas in that language. It'll be a great motivation to keep learning the language!