I lived in Japan for 16 years, China (mainly Beijing) for 20, and Mongolia for 8. Currently I mainly do edits adding Mongolian to translations into other languages, or, on occasion, correcting and adding Chinese and Japanese translations.
I've found many problematic areas in Wiktionary. These include:
The treatment of "Chinese" as a single language with many "dialects". (This is a controversial topic and I will not elaborate.)
The inclusion of various marginal words in Japanese, especially terms from English. Since some Japanese love to lard their speech with English words (modified to fit the phonology of Japanese and usually written in katakana), often in order to sound "sophisticated", it's possible to include all sorts of terms that have very little actual currency in Japanese. A rather extreme example I have found is "defenestration". This word is mostly associated in English with certain historical events (e.g., the defenestration of Prague) but does have some currency as a general term for summary and undignified dismissal from a position or status. The names of the historical events have conventional Japanese translations (which, to be fair are quite stiff kanji-based terms only likely to be known to history buffs or high-school students), but there does not appear to be a Japanese word that can directly or conventionally render the more modern usage. Despite this, some user listed デフェネストレーション (defenesutorēshon) as the Japanese translation of the English word "defenestration" -- while strangely ignoring the conventional Japanese names for the historical events. The only discernible basis for listing デフェネストレーション as a Japanese word is a Japanese Wikipedia article on デフェネストレーション (see https://ja.wikipedia.org/wiki/%E3%83%87%E3%83%95%E3%82%A7%E3%83%8D%E3%82%B9%E3%83%88%E3%83%AC%E3%83%BC%E3%82%B7%E3%83%A7%E3%83%B3. However, it's clear from the Japanese Wikipedia article that 1) it has been directly translated from the English article, and 2) デフェネストレーション was only chosen by the translator as a tentative title. Of course, it is possible that certain Japanese people with a literary bent or a predilection for using English words might use the term デフェネストレーション, but at present it is only by a very long stretch that デフェネストレーション could be regarded as an actual Japanese word. While this is an extreme example, similar phenomena are common in Japanese -- any English word is available as a potential Japanese word (e.g., a fancy alternative to the common term, or an early borrowing before usage settled on the modern conventional term) although such words have very limited currency within Japanese itself.
The Khalkha, Cyrillic-centred nature of "Mongolian". For many editors, Mongolian is defined as the standard language of the Mongolian State. Editors mostly ignore Inner Mongolian usages and also often ignore the traditional Mongolian script. (Of course, Kalmyk and Buryat, which are the literary creations of Russian linguistic policy, have their own separate entries, totally unrelated to Mongolian.) I firmly believe that Inner Mongolian usages should not be ostracised, however poorly regarded they are by Khalkha speakers in Mongolia.
Wiktionary is orthographically based, which causes problems in Japanese. The same word may be written in different ways, and conversely, the same characters might be read in different ways. See the entry for kingfisher to see how orthography and readings can be intertwined in complex ways. For Japanese, at least, entries should possibly be pronunciation-based, with alternative orthographic forms given as "also written as" (for an elegant example of this, see https://en.wiktionary.org/wiki/platypus). Another problem is the modern tendency to replace kanji that are not in standard-use kanji tables with hiragana or katakana, which some Japanese find objectionable. (This is possibly why one Japanese user replaced ブドウ糖 as a translation of glucose with the historically correct 葡萄糖. Unfortunately, this fails to tell the ordinary Wiktionary user that ブドウ糖 is overwhelmingly the most common usage nowadays. Such is the issue of script in Japanese.) (Note: Chinese presents different problems -- see comment on Chinese above. Thankfully, Chinese entries at Wiktionary always include the pronunciation, avoiding the trap of taking dialect terms, reading the written form in Mandarin, and claiming them as "Chinese" -- a common phenomenon among Chinese speakers. The fact that a particular plant or animal, etc., has a certain name in a non-Mandarin dialect does not mean that it should be regarded as a word in Mandarin Chinese. Although, to be fair, this phenomenon is one of the reasons Chinese see their language as a single language.)
At times I've become impatient with some additions by prolific early editors who clearly had a very poor knowledge of the languages they were adding translations for. User Atitarev blocked me after I continually criticised some of his early edits containing egregious errors. (My main beef with Atitarev was that, despite his expressed contrition for his earlier errors, he did not feel the need to go back and systematically correct his old edits -- obviously too much trouble as they stretched into the thousands.) I still keep coming across less than optimal translations from Atitarev and other early users.