Support for multiple captions languages

Some sources typically include multiple languages. You can include multiple languages in the output as follows.

Source captions	Output captions	Result
ARIB	ARIB (which is the only option for ARIB sources)	This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages.
Embedded	Embedded	This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any of the languages.
Embedded	Another format	You can specify which languages to extract and include in an output.
DVB-Sub	Another format	If you have DVB-Sub source and want a different format in the output, you can specify the language to extract from the input and the language to include in an output.
DVB-Sub	DVB-Sub	This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages.
Teletext	Teletext	This combination is performed as a passthrough. Therefore, all the languages that are in the input are included in the output. You can't remove any languages. In fact, the entire Teletext content is included in the output; you can't remove out any of the pages.
Teletext	Another format	You can specify the language to extract from the input and the language to include in an output.
Any other combination		For all other sources, you always specify the language to extract from the input and the language to include in an output, regardless of the source format and output format.