Is the title, Tanaka-kun Is Always Listless, a good translation? I have recently started watching the 2016 anime, Tanaka-kun Is Always Listless ( 田中くんはいつもけだるげ ).  Plugging the Japanese into the Google Japanese-to-English translator, it comes out as "Tanaka-kun is always wonderful".  One possibility is that there is a Japanese homonym that can mean either "listless" or "wonderful".  That seems like a pretty big spread.  But I guess if "bat" can either be a crafted wooden stick or a blind flying mammal, it certainly is a possibility.

Another possibility is that the translation does not capture the full Japanese meaning.  Perhaps the implication is more on the lines of "wonderfully listless", which actually sort of fits the series.

A third possibility is that there is not really a concept in English that matches the Japanese.  Having watched the first two episodes, I know choosing "listless" to describe Tanaka was an accurate choice.  So maybe the translators chose a single English word that fits his personality and did not try to match the Japanese exactly.
Not only it's a good translation, but it's also the correct translation.

Logan has already explained the construction of the word


  けだるげ is technically a combination of けだるい and 気 using this somewhat uncommon construction.


Using this as the base, searching for the definition of けだるい returns:


Jisho: languid; listless
Japanese Wiktionary: listless, lazy


The conclusion is, echoing Senshin's comment:


  The English title is a literal translation of the Japanese title; there's nothing to read into here.