Please consider the following email response given to @Liuxinyu970226 when they asked certain linguistic expert about their opinion on the matter: https://imgur.com/a/YT8bnzJ (I am not sure whether sufficient permissions have been obtained by the user for me to link the mail on the public internet but let's just look at it for now)
I believe there is not so much difference. If I remember of everything after few years of try, some argued that any of them can't be used in Wikimedia because they are meta-languages, not languages,, because mvf, based on Chakhar/Chahar, and there are other languages after some definitions. People opposed said that's the rule to note create new meta-languages entries, only languages are accepted.
There is already mn (also a meta after those norms, but in Wikipedia, match, official Khalkha/Halha (khk) dialect from Outer Mongolia (or Mongolia state) and is wrote Cyrillic (All Outer Mongolian people don't understand traditional Mongolian, that's mainly used in art there, but will should come back as official script in about ten years).
mvf is the official written (in Mongolian script) and spoken language by millions of people in inner Mongolia, spoken at inner Mongolian TV channels, wrote in newspaper, road signs, learnt at school, spoke in buses/train station for station/warnings, museums, etc,
The current norms say that's a meta-language, not a language, some spotted, errors in current norms.
All this Mongolian varieties are not very far each from other anyway. If we consider mvf a metalanguage, we should do too for ja, as Kansai Japanese (for example) use lot of words, tones, grammar rules different from official Tokyo japanese. The same for standard mandarin (cmn) vs NW/NE/SE/SW mandarins (SW one is one of the ten most spoken languages on earth).
With my very very low knowledge in Mongolia I was able to exchange using Khalkha Mongolian (khk) official language from outer Mongolia (most courses are from this dialect, and I only know people of Outer Mongolia in France), with people from south of inner Mongolia,, (mvf), from Ordos and Chifeng. They understood everything. As far I searched for words in dictionaries referring to cmg Outer mongolian one using both cyrillic Mongolian and traditional Mongolian scripts or those using mvf I didn't found differences, I suppose there are at least some in vocabulary usage, but there are dialects of the same language.
Mongolians used lot of scripts in their history, first one (since ~13th century) and most longer user one is traditional mongolian script, that is derived from uyghur script (uyghurs use arabian script adapted to turkic language in China today).
There are other varieties of Mongolian, that are not grouped in mn/mvf, and are really different Mongolian languages, not understandable by khk/mvf :
- Buriat (bua, with subode, bxu (China), bxm (Mongolia), bxr (Buriatia (russian federation)
- Kalmyk (xal) also called oirat, mainly spoken in China (mainly Qinghai and Xinjiang provinces) and in Kalmyk Republic, in eastern Europe
- Daur/dagur (dta) in most north-east part of inner Mongolia and at East of Buriatia
- Moghol (mhj) in Herat province, Afghanistan
There are few other, spoken by more little groups
- Monguor/Tu, in Qinghai province, China (influenced by Tibetan language)
- Yugur, in Gansu province, China
So, we already have these:
- Fully supported everywhere: Wikipedia, MediaWiki, Wikidata, language-data, and translatewiki:
- mn - Mongolian, Cyrillic script. (Maybe not perfectly standard, because it should be khk and mn is a macro language, but that's the de facto standard for the standard language of the Republic of Mongolia. We have the same issue with Albanian and Estonian, and it's not really a disaster.)
- xal - Kalmyk, Cyrillic script.
- bxr - Buriat, Cyrillic script.
- Supported in language-data, translatewiki, and incubator:
- mvf - Mongolian, Mongolian script. There is some activity in the Incubator. There's no activity in translatewiki, unfortunately, but if anyone is interested in contributing, it's immediately available, and if someone translates enough messages, it will become fully supported in MediaWiki, and no special treatment for Wikidata will be needed. Till then, it's totally fine to add it for Wikidata.
Now the question is whether cmg is still needed separately. If it's substantially different from mvf and names would be written differently, then I guess it's fine to add it. But if the names are written the same way in cmg and mvf, it makes more sense to me to just keep using mvf.
I first created this because Mongolian in mongolian script was rejected in all it's codes, but it could be usefut to referring to this code for name of medieval Mongolian people, as the notion of mvf didn't exists at this time, this could avoid anachronisms.
@Popolon This request doesn't include any samples, can you add them in the task description?