In Android, you can specify the texts in the default locale in res/values/strings.xml. Additional translations can be added for new languages in res/value
If you also want to let other people contribute and have a web site you can use the open source TranslateApp-tool.
It keeps track of what is translated and not, you can also update the default language and say if translations should be invalidated of not.
https://bitbucket.org/erik_melkersson/translateapp Note: I am the author of the tool. Pull requests with updates are welcome. I actively use the tool myself.