To add a flag to a mobile style, you need import vBET template:
1. Open AdminCP->Styles & Templates->Style Manager->Default Style->Edit templates->vbenterprisetranslator_flags.
2. Change value Style from Default Style to your mobile style.
3. Save the template.
If you want to add other vBET template (e.g. add a flag to translated messages) then import other needed vbenterprisetranslator styles.