Tocharian is not in the same family (Sino-Tibetan) as any of the Chinese topolects -- it's an Indo-European language spoken in Xinjiang.

Small correction: it was spoken in Xinxiang. A long time ago

There is something puzzling about the existance/presevation of the word in Tocharian B. The tocharian people were living in the tarim basin, a dry land, far away from any ocean. Were there any salmons there?

The Tocharians used an Indic script. We know what the letters mean for Indic languages, so we can get a pretty good idea of what Tocharian sounded like. Pretty good.

Not perfect, though. For example, Icelandic and Old Norse are very close in terms of how they're written, but (IIRC) have pretty substantial differences in pronunciation.

Yep. It's likely that Icelandic speakers can read Old Norse, especially with footnotes, but they most likely wouldn't be able to understand the sagas if they were spoken aloud. And a lot of the reason Icelandic is as conservative as it is is because of a push towards purism from Danish influences in the 19th century.

All the Scandinavian languages can be read by speakers of the other Scandinavian languages, somewhat accuately, in written form, given enough time, cursing and crying is invested into doing it. Icelandic and Faraoese are quite different from the others, but they're not THAT hard to understand when written down.

Speakers of Danish, Norwegian and Swedish can usually talk to eachother without major issues although the kids seem to be preferring to speak English nowadays.

Spoken Icelandic or Faraoese on the other hand? I usually manage to get a single word or phrase. The rest is gibberish.