WIP: Missing Language id in certain cases

[DavideIadeluca]

This PR tries to address an issue when fof/discussion-language is used in combination with fof/follow-tags.

Problem Description:

• If a user follows a new tag and leaves the discussion language to default (default in this case is the same as the language set in the UI in general), no language id is passed and the field dl_language_id is NULL in the tag_user table.
• This issue doesn't happen when the user opens the LanguageDropdown inside the SubscriptionModal and clicks on any language. This is because the onclick method of buildDropdownContent is called.

Summary:

• Add fallback language (as set in the UI) in requestData if this.language() is null

Notes:

• This feels like a very 'hacky' fix to me because there are quite some presumptions taken (as far as I understand) for this fix to work as intended. I guess with this fix there should be at least a language in dl_language_id instead of it being NULL. During testing though the language id was correctly passed after the change.
• Also, we need to look at how to populate the fields retroactively where dl_language_id is NULL to prevent incorrect notifications from being sent (in my case the bug was discovered with emails). I'll try to come up with a CLI command and propose another PR. Edit: #54

[imorland]

I can see where you are coming from here, and the underlying problem. However, the intention is that if dl_language_id is null, then the user does not want to restrict notifications to a particular language, and will therefore receive notifications for any language.

[DavideIadeluca]

Okay, so I think I know what's going on now. By default, the setting to show "Any Language" as an option is enabled. Then, when following a tag, the option "Any language" is also selected by default.

In this case, it makes totally sense to don't pass any language id. And if the user only wants to follow a certain language, then the onclick handler is called and the respective language id passed.

The confusion stems from when the setting to show "Any Language" as an option is disabled. In this case, a language is visually already "selected" in the dropdown, but no onclick handlers are being called, when left unchanged, which are needed for the id to be passed as far as I understand.

I guess this would a case that needs to be covered?

[imorland]

Superseded by https://github.com/FriendsOfFlarum/discussion-language/pull/55