Here is one word: 不格好{ぶかっこう}な
What does this word mean
When 不格好な is looked up in online Japanese dictionaries, the word describes something that is awkward, clumsy, poor in appearance, and improper as it appears to be.
Basically, 不格好な refers to the negative appearance or condition.
When 'clunky' is looked up in bilingual dictionaries, 「不格好な」 was similarly found in Longman English-Japanese Dictionary (2007). This dictionary was the only physical dictionary that I have had those words. If you have this dictionary, see page 293.
Despite the words are linked by the dictionary, I feel these words are not quite interchangeable between two languages. Additionally, 不格好な is not used for describing slow movements or reactions (sluggish). There is another word for that.
However, these words could agree with each other, when referring to awkward or unsophisticated appearance.
Where does the word fit
There are at least two instances that the word is used in Japanese articles on the web.
Walkmanアプリのみフラット化されている不格好な状況ですが、アルバムやムービーなどのアプリもフラット化されるのは時間の問題と思われます。
From Xperiaの「Walkmanアプリ」がロリポップ対応。フラットデザイン化を達成 – すまほん!!
今までずっと身近にあったものが存続の危機を迎えたときによく見られるパターンが、ここでも繰り返されている。やや不格好で単純なこのソフトウェアが、実際にはけっこう便利なものだと、ユーザーがにわかに気付き始めたのである。
From 「Windows」PCは死なない--「ペイント」もまたしかり - CNET Japan
Even without translation text in English, we could tell that both articles use 不格好 to describe awkward or unsophisticated condition of particular software (Xperia, Walkman apps; Windows, Windows Creators Update).
Therefore, 不格好 is compatible with "clunky apps".
What about "clunky translation"
From my quick googling, the phrase 不格好な翻訳 did not return any relevant result. Moreover, the search engine even misunderstood the query as "translation for 不格好な". So far I have never seen this kind of usage.
Therefore, 不格好 is not compatible with "clunky translation".
To describe "clunky translation", I'd suggest to use 不自然{ふしぜん} that means unnatural or artificial; or perhaps a simple word, おかしい that means strange, weird and possibly awkward.
As a result, the following are possible:
- 不自然な翻訳 or 翻訳が不自然
- おかしな翻訳 or 翻訳がおかしい
Another word besides 「不格好」 is 「ださい」(not to be mistaken by suffix phrase -ください). However, 「ださい」 could include the meaning of criticism rather than to simply describe negative appearance or condition itself.
Not quite apt, but 「ださい」 may be compatible with the word "clunky" in American English that is used as slang - Not stylish or attractive.
Yet another word 「イマイチ」 means not very good or something is lacking. This word merely hints something is less satisfactory, but that alone does not necessarily describe the negative appearance or condition itself. Not quite apt either.
Summary
The following are suggested sentences for "clunky apps" and "clunky translation":
- このアプリは 不格好で、 使いにくい・使いづらい。
- この翻訳は 不自然で、 読みにくい・読みづらい。
- この翻訳は おかしくて、 読みにくい・読みづらい。
Above all, this answer suggests to use 不格好(な) for "clunky apps" as well as 不自然(な) and おかしい(おかしな) for "clunky translation". There is no single word that fits for both use cases.
References
- Longman English-Japanese Dictionary (2007)
- 不格好な - Weblio辞書
- 不恰好・不格好(ぶかっこう)とは - コトバンク
- ぶかっこう【不格好／不恰好】の意味 - goo国語辞書
- Clunky - Collins English Dictionary
