My open source Android application has internationalization done the Android way, with strings.xml files.
The community has many people from many countries, and they are willing to contribute/improve translations using a collaborative website.
There is Launchpad but it only supports the gettext format so we would have to use scripts, not very convenient.
There is Crowdin but somehow this website seems dead, nearly no projects, and the download links do not work. Actually we started using Crowdin but all download links fail to give any strings.xml file back, see here.
What website is convenient for translating open source Android applications?