ALT works for me.

ALT+SHIFT+B doesn't work for me either.

Another thing to consider here: https://meta.wikimedia.org/wiki/Tech#Meta-wiki_translation_tool_hijacking_keys

Quoting:

As the translation tool on meta binds alt for its own purposes, editing on macOS, which uses the same key for entering special characters, is a major pain. A solution would be greatly appreciated.

It might be worth it to perhaps look at other key combinations.

Testing this on Firefox (106.0.5 (64-bit)) on Linux.

• ALT works if there are insertables in the translation editor.
• ALT-SHIFT-B works if there is content in the translation editor, and the summary textbox is enabled.
• CTRL-ENTER works
• ALT-SHIFT-Dworks if the current translation has the "Skip to next" button is present. This key doesn't actually skip, but highlights the button. ENTER can be pressed to actually perform the operation.