How to spot (if possible) if a final 了 is part of an omitted 要 in a 要...了 construction or simply a past information?
了 in "我去中国了" does not emphasize it is a past or future action in absent of context.  Consider the following:

我去年去中国了  - I went to China last year
我明年去中国了  - I will go to China next year  

Both are legit and 了 changes depend on the content, althought a native speaker will say:  

我去年去了中国  - I have been to China last year
我明年(要)去中国了 - I have to go to China next year