Writing in another language is a great experience. I love to use expressions from a non-mother tongue as playing with them seems to be much easier as with the language I was grown up. I don’t know why it is so – but somehow it is.
English for example is a very smart language – with changing the words’ positions within one sentence you can get wonderful strange variations. Sometimes it sounds more British, sometimes more American, sometimes Irish and sometimes just weird. English is also perfect for describing melancholia. It is a kind of happy-sad thing that is in the language.
But probably the best thing about using a language as a non-native speaker is: you are allowed to make mistakes, and most of the natives think that it sounds quite sweet talking a bit Gerlish, Franallemd, Espallemán etc.
As a conclusion you must say: writing in a foreign language has almost advantages, and only a very little handicap: you need to know enough words before starting, or a pretty good dictionary that helps you with your translations …