Feature request: Subtitle Custom format

Is there an existing issue for this?

• I have searched the existing open and closed issues

Is your feature request related to a problem? Please describe

The user is not able to create a custom format condition that they can use to filter by subtitle language (like they can with audio language)

Describe the solution you'd like

A condition that allows the user to match against one or multiple subtitle languages

Describe alternatives you've considered

No alternatives considered

Anything else?

The newznab protocol has attribute just like the attribute that is currently used to filter by language