Yes, it is.
There is no other answer. When you translate from one dialect in a given language to another dialect of the same language, you are doing an act of translation.
Do you think you would be able to understand and read a mystic dialect text from the 15th century? Would you know what demyth or kyndely is?
Read this for example:
For English people it might be guessable, but not for speakers whose native language is not English.
Now take a look at the translation by Mirabai Starr:
There you go. A translation of a passage of the Julian of Norwich book, which uses a Chaucer-like Middle English dialect, into modern day English (dialect). Translation is a wonderful thing isn’t it. It bridges languages and even dialects and helps information get transmitted.
Now you may say that this is not a valid example, because these dialects are not separated in space, but in time, which is a good argument.
But, aren’t dialects languages themselves? Is there a clear distinction between what is a language and what is a dialect?
And, how come some dialects like Mandarin & Cantonese in China, or Furlan & Sicilian in Italy are so vastly different from each other, while languages like Norwegian, Danish and Swedish are highly similar but are still considered separate languages? Is the concept of a dialect and language just an arbitrary marker for sociopolitical status?
Would love to read your thoughts on this!