In Query Service typing a variable name outside of [a-zA-Z0-9_] results in no syntactic coloration and no autocomplete, although the SPARQL specification is quite extension about variable names and Blazegraph accepts any variable name inside the Unicode BMP (Basic Multilingual Plane). Example.
I proposed – and it was accepted – to CodeMirror to extend syntactic coloration to any SPARQL variable inside BMP, see PR #5935. It should appear from version 5.49.0+ of CodeMirror.
I propose in this task a patch to enable autocomplete for any variable name inside BMP.
PS: according to some tests, Blazegraph and/or another piece in the Query Service does not accept variables names outside BMP; for instance try with 𠇲 (U+U+201F2 CJK UNIFIED IDEOGRAPH-201F2), so this task limits itself to BMP. Another task should be opened for astral planes (above BMP).