"$<-" fails (invalid subscript type 'language')

I would expect the following to behave identically:

tv <- c(a="dsf", b="sss")
tl <- list(232)

`$<-`(tl, tv[[1]], "sdfdsfdsfsd")

Error: invalid subscript type 'language'

tl$`tv[[1]]` <- "sdfdsfdsfsd"
tl

[[1]]
[1] 232

$`tv[[1]]`
[1] "sdfdsfdsfsd"

So what is relay going on? In one case the name is expected, in another case any
"language" object would work?

If you insist, you can do things like

eval(bquote(`$<-`(x, .(as.name(tv[[1]])), 4343)))

or similar constructs using substitute().

However, the whole situation suggests that you are really looking for
methods for "[[<-".