I have seen my bug similar to the PT (Portuguese) and this bug already fixed in latest update from Solus repository, but it don't work for VI (Vietnamese), i can change the input method by press Keyboard Shortcut Super + Space but nothing change in Keyboard Layout Applet, it show English (US) all the time. Of course I have already installed Ibus - Unikey package from repository and add it to Input Sources in Region and Language Setting, also add it in Ibus Preferences.
I don't know why this bug were fixed in PT (Portuguese) Language but not for VI (Vietnamese). So I hope Solus Developers will fix it as soon as possible in the upcoming update, I just installed Solus 4 yesterday alongside with Windows 10 and I really want Solus is my main OS for stable to use in the long term, I love the way Solus make the OS so simple, beautiful, elegance, fast, lightweight and personalize. Thank you veru much to Solus Project for contributing to the world a good OS.
p/s: Sorry for my bad English