expl3: partially expand an argument

Question

I wish to assign a \crefname with dynamical strings. With \exp_args_generate:n { xVV }, I ended up with something like:

\exp_args:NxVV \crefname {\__my_countername: }
                         {\csname my@cref@\__my_countername:\csname\languagename ABBR\endcsname @name\endcsname}
                         {\csname my@cref@\__my_countername:\csname\languagename ABBR\endcsname @name@plural\endcsname}

Here \__my_countername: is the counter's name, such as theorem. \csname\languagename ABBR\endcsname is a conversion from string like english to EN.

However, this expands the arguments too deeply that the strings are no longer dynamic with respect to the context. To be clear, I wish the arguments to be expanded to:

\crefname {theorem }
          {\csname my@cref@theorem\csname\languagename ABBR\endcsname @name\endcsname}
          {\csname my@cref@theorem\csname\languagename ABBR\endcsname @name@plural\endcsname}

That is, to make \__my_countername: expanded while keeping \csname\languagename ABBR\endcsname untouched, since it should receive \languagename from the context. Would that be possible?

I tried to use \noexpand, but probably misused, which leads to an error with no warning text.

(Please forgive my terrible mixture of expl3 and LaTeX2e code, I'm not familiar with expl3 and it would be much easier for me to use a little LaTeX2e code for some tasks)

Answer 1

Became too long for a comment:

If you want to expand \__my_countername: and keep everything else unexpanded, then you can use x expansion in all arguments, and keep other tokens from being expanded with \exp_not:N:

\exp_args:Nxxx \crefname { \__my_countername: }
  { \exp_not:N \use:c { my@cref@ \__my_countername: \exp_not:N \use:c { \exp_not:N \languagename ABBR } @name } }
  { \exp_not:N \use:c { my@cref@ \__my_countername: \exp_not:N \use:c { \exp_not:N \languagename ABBR } @name@plural } }

(I replaced \csname ... \endcsname with the more expl3-y \use:c { ... }).

The above would expand only the three \__my_countername: (which sounds like it's misnamed). But that's doing the same work three times, so you can instead define an auxiliary macro and expand \__my_countername: just once, making the code a bit faster, and a lot easier to understand:

\cs_new_protected:Npn \__my_crefname_aux:n #1
  {
    % In this macro, #1 is \__my_countername: expanded
    \crefname {#1}
      { \use:c { my@cref@#1 \use:c { \languagename ABBR } @name } }
      { \use:c { my@cref@#1 \use:c { \languagename ABBR } @name@plural } }
  }
% then use it as:
\exp_args:Nx \__my_crefname_aux:n { \__my_countername: }