According to https://learn.microsoft.com/en-us/typography/opentype/spec/otff#collections,

An OpenType Font Collection (formerly known as TrueType Collection) is a means of delivering multiple OpenType font resources in a single file structure. The format for font collections allows font tables that are identical between two or more fonts to be shared. Font collections containing outline glyph data (TrueType, CFF, CFF2 or SVG) are most useful when the fonts to be delivered together share many glyphs in common. By allowing multiple fonts to share glyph sets and other common font tables, font collections can result in a significant saving of file space.

On Ubuntu 20.04 some of the OpenType font collections include Noto CJK fonts (which cover East Asian scripts):

gabe@gabews:/usr/share/fonts$ find . -name "*.ttc"
./opentype/noto/NotoSansCJK-Thin.ttc
./opentype/noto/NotoSerifCJK-Bold.ttc
...

.TTC Collection files contain TrueType glyph outlines (sfntVersion == 0x00010000)
.OTC Collection files contain CFF or CFF2 outlines (sfntVersion == 0x4F54544F or 'OTTO') *

• Note CFF fonts are not supported yet (#20744)