English is used instead of the base language for missing pt-BR

[biodranik]

There is a logic now that our clean_strings_txt cleans up similar sub-languages translations, and twine properly supports it by generating the base language for iOS. For example:

[type.historic.fort]
en = Fort
...
pt = Forte
pt-BR = Forte
ro = Fort 
...

becomes

[type.historic.fort]
en = Fort
...
pt = Forte
ro = Fort 
...

and works correctly. The bug appears when that translation is referenced in another translation:

[type.someothertype]
ref = type.historic.fort

Then instead of pt Forte the wrong en Fort is generated.