I knew this film since 2009 through one man called usually as Birubir. At that time he was quite known for uploading many Russian films with English subtitles in high definition, although those years when the quality of YouTube' clips were very limited. I downloaded regularly his videos at YouTube, Stagevu and Veehd channels. Of course, the two behind sites are down nowaday.

Puppet is a difficult technique, so I don't like watching most of these films. HOWEVER, The Magic Lake surprised me with its excellent aesthetic. Even the music part, I see similarities with the music in Chinese cinema at that time. This : Laoshan Daoshi

Leopold has the best songs, and they're usually the highlight of this series for me. This episode has great music all around.

In other respects: the character design is nice enough and there are a lot of gags (hearkening back to what Soyuzmultfilm's production was like in the late 1930s), but the execution is kind of sloppy (and I thought so when I watched them back then, too! There were lots of mistakes I would notice). The size of the mice varies hugely again - from being almost as big as Leopold when they're on the motorcycle, to being the size of his feet when they climb up his trousers at the end!

Coincidentally in Canada there is also a music band who is called as «Liu Brothers» (by Chinese fans) or «Lưu Triplets» (by Vietnamese fans). They are Vietnamese-Chinese men but born in Canada. So the original text is called as «劉氏四兄弟» or «劉家兄弟故事».

https://tuoitre.vn/ba-anh-em-trai-dep-ho-luu-den-tphcm-568332.htm
https://vnexpress.net/anh-em-ho-luu-chung-toi-hanh-phuc-vi-co-nhieu-fan-viet-2877519.html

I remember really loving the opening song in this one... though I thought the rest of the film never quite matched it.

It always bugged me how the mice constantly change size relative to Leopold in this. Especially at 6:20 when they suddenly become really huge!

This movie, after some consideration, I decided not to translate. Those are just rambunctious discussions at the dinner table, so it is fine to leave them in Russian or English.

In my opinion, that is fine to leave most of it as is, just footnotes. However, fortunately characters "Veselchak U" and "chatterbird" have equivalent words in classical Vietnamese language : Tễu (笑 / "laugh" ; who has a cute body and funny personality), Liến Thoắng (連通 / "continuous communication").

https://tve-4u.org/threads/alisa-phieu-luu-ki-kir-bulychyov.36569/

Nice book! Thanks for that link.

Yes, I found it hard to translate as well. But if you're trying to do it, I think you should use the latest English subtitles that are here, rather than the older ones elsewhere online (a lot of which have mistakes).

By the way, regarding the names of the characters:
(Professor) Selezniov = slug
(Captain) Zelyony = green
Gromozeka = the root is "grom" (thunder), probably because of how boisterous he is
Veselchak = happy person (he's often smiling and eager to please in the film)
(Professor) Verhovtsev = higher
Ptitsa Govorun = talkative bird (I was fortunate that English already has the word "chatterbox", which I could easily modify into "chatterbird")
Glot = possibly from "glotka" (throat)

Most of these I kept as is, but I did translate "Green" because that's a common English surname too.

I have watched this movie on Vietnam Central Television (VTV1, "The Little Flowers" program) since I was very young, of course only on black-white TV. This is a very challenging movie about translation. Here is the film story (фильм-сказка) : http://www.barius.ru/biblioteka/book/852