AFAIK input methods are mostly useful for ideographic languages like CJK. Do you really need that for Indian languages, central asian ones or Russian that are alphabetic ones and include not that many characters?
Just a reminder, under X using the default evdev driver that applies the RMLVO (Rules, Model, Layout, Variant, Options) template you can set your keybord(s) to any combination of values found in /etc/X11/xkb/rules/evdev.lst.
You can have several keyboard layouts. For instance you can set XkbLayout to "en,in" for English, Indian, XkbVariant to ",kan" for Kannada language and include in XkbOptions grp:<something> and possibly lv3:<something> to choose your way of switching keyboard layouts and possibly how to choose 3rd level.
About ctrl+shift+u: in this editor pressing them together displays
u (as in Unicode), then typing the digits one at a time then pressing [Enter] displays the relevant glyph if available. This is how I have put the "grinning cat face with heart shaped eyes" (U+1F63B) in my signature. Here[1] the cat face is smiling instead (U+1F638):
😸
[1]Can be saved here only if this editor is in advanced mode due to a bug already reported to Jeremy @LQ.
PS The settings used for X can also be used in a framebuffer, provided that the framebuffered terminal also uses the RMLVO scheme, through the libxkbcommon library. This is the case for instance of kmscon, provided by @
http://slackbuilds.org