The fix is to listen to the config change event and register new completion providers for the newly added languages in includedLanguages

I take a look, I saw this in other extensions and it isn't that hard.

Yes, not hard at all. Feel free to submit a PR

I can't get it to work, reload or not.

It works for me, for example when I add XML files manually to emmet. And those are the same methods, so when it works for the standard languages, it should work for custom ones too.

I still didn't see Emmet proposals after adding this setting. Should those proposals show up in the suggestion window? @ramya-rao-a

The reason why @roblourens and @rebornix were not able to get any suggestions was because they hadn't set emmet.showExpandedAbbreviation to always

I had initially introduced always as an option to emmet.showExpandedAbbreviation setting because, back then the emmet suggestions (not css) were too eager and showing up for every letter that was typed (because every word/letter was a valid abbreviation. eg abc -> <abc></abc>)

But in the last month there have been many improvements and now non css emmet suggestions only show up if the word is one of the commonly used html tags or is a valid abbreviation with operators like >, $, * etc. or is a custom emmet snippet.

This "always" vs "markupAndStylesheetOnly" option may not be required any more

On spending more time thinking on #29968 (comment), I feel its not wise to remove the "markupAndStylesheetOnly" option altogether.

There can still be cases where emmet suggestions showing up in wrong places annoying users.

Instead, as a middle ground, we can change the default for this setting to always

This way, the moment a mapping has been added to emmet.includeLanguages, emmet suggestions will show up and the command Emmet: Expand Abbreviation will use the mapped syntax.
Anyone finding this as noise, can update emmet.showExpandedAbbreviation to inMarkupAndStylesheetFilesOnly. The command Emmet: Expand Abbreviation will continue to use the mapped syntax.

This is done with dd7adcc