1) We aren't talking about 'Western' sets of glyphs, but Latin typefaces that include all the Latin characters, accents, ligatures for all languages that use Latin characters (including Vietnamese, Lahu, as well as Amerindian languages and African languages that use Latin script). The basic font files use one-byte encoding, MEPS has a Unicode conversion algorithm that translates Unicode/UTF-8 input (that might include precomposed accented characters) into the glyph sequence generated for PostScript output.
2) When talking about Latin fonts, MEPS used two different sets of fonts. The newer ones (those used mostly today) were purchased from URW (apparently the full URW TypeWorks collection released in 1994), and those have names starting with WtU followed by the font name (WtUStoneSerItcTMed) and started to be used in 1996. The older ones are the result of Watchtower's own digitization process in the early days of MEPS. Most of them have commercial counterparts, but some glyphs are pretty much different and the type production departament of the Watchtower has done a pretty neat job.
3) The fonts used for the Bible are not the same in every language. English uses WtHelvetica for sans-serif type and WtIon (a slightly lighter version of WtIonic, the font used to compose the Daily Text booklet) for serif type, but most other languages have WtRegalII (the font used in forms and talk outlines), few exceptions use WtEgyptian (German, Greek, Portugese, Slovak), WtUBookmanItcTLig (Polish), WtCenturySchoolbook (Vietnamese), WtUStoneSerItcTMed (Turkish) and even spotted a WtGaramondNew in the Czech edition. Probably by having this new set of fonts they want to use a modern set of typefaces to further distinguish this new revision and use the same fonts in every language.