I have just tested translating a string with "å" on my demo installation and there aren't any problems. The string was translated fine.
Make sure that both your translation.ts file and tpl file where you use i18n operator, are saved as UTF-8.
It's not enough to just put encoding="utf-8" at the top of the files. They need to be saved as UTF-8 too. Any better text editor allows you to save your files in UTF-8 encoding.
I can't say for sure where it is written, but I do remember reading that from version 4.0, eZ Publish requires practicly everything to be UTF-8 encoded. That includes, database, templates, translation files.
There is a paragraph in upgrade docs about DB needing to be in UTF-8: