Since T40551 have been resolved, it is possible to have per-language bold/italic button variants. But the only two languages using this are currently English and German. Do we really need to ask language by language, when we've been through all this with the Vector edit toolbar (see e.g. T25625: use B and I as icons for Bold and Italic in the Hebrew Wikipedia in the enhanced toolbar in Vector, T25911: Czech icons for bold and italic text should be B and I, T26188: Bold and Italic Icons in Vector toolbar to 'B' and 'I' in Malayalam etc.).
We already have https://commons.wikimedia.org/wiki/WikiEditor_Toolbar_Icons#List_by_language -- cannot we use that?
See also: https://usability.wikimedia.org/wiki/Opinion_Icons