I would really like to use TeXmacs for preparing linguistic publications, which may include multilingual text. TeXmacs does not seem to support Unicode combining diacritics. E.g. when I paste `бе́ля` in a TexMacs document, the accent is rendered as a full-width character between `е` and `л`, no matter which font I choose. Typing `⌘' e` (Latin `e`, not Cyrillic as above) renders `é`, but it does the job only for precomposed Unicode characters known to TeXmacs. OpenType `gpos` table has (e.g. in Times New Roman) a `mark` feature, specifying a "base" mark-to-base anchor point on Cyrillic vowels and a "mark" mark-to-base anchor point on U+0301 (combining acute accent), so the renderer can position the mark correctly above the preceding character. However, TeXmacs reimplements most of font rendering instead of reusing Harfbuzz which implements countless script-specific shaping quirks using OpenType tables. IMHO it's a Sisyphus' job.