You can override the default android:label=“@string/app_name” for different languages this way: (tested on Unity 5.5.1p2)
Unity creates a strings.xml file by default which contains the Product Name that you set in the Unity Editor in Player Settings > Product Name That string you mention is found in that strings.xml resource file (which is found in the res/values/ folder in the generated Android project).
To add support for more locales, you must create additional directories inside res/ each directory’s name should adhere to the following format:
resource type-b+language code+country code
For example, the folder values-b+es contains string resources for locales with the language code es (Spanish), inside each folder will go a strings.xml file with the texts on each language.
You can add the new locales inside your Unity project creating the following directory structure:
Assets
-> Plugins
-> Android
->res
->values-b+en
->strings.xml (with your text in english)
->values-b+es
->strings.xml (with your text in spanish)
->values-b+fr
->strings.xml (with your text in french)
...
...
...