In which form string resources can be uploaded?

You can upload your strings directly from you IDE using our available libraries. The reason behind this is the advanced analysis of translatable strings. Localazy will find all strings and will also recommend ignoring common private strings if they are not flagged.

Is this way of uploading useful also for apps which already have translations?

Of course, this works for both starting and enrolled apps. Moreover, you can easily migrate all your work into Localazy and finish your current unfinished translations sooner thanks to Localazy ShareTM.