Change th-TH culture to th

Web browsers (at least Firefox and Chromium) only send th in the Accept-Language header, leading ASP.NET to select it as the current culture. This leads to Humanizer failing to find the resource and consequently falling back to the default culture. Renaming the resource files to the more generic language/culture specifier fixes the issue.

Here is a checklist you should tick through before submitting a pull request:

[x] Implementation is clean
[x] Code adheres to the existing coding standards; e.g. no curlies for one-line blocks, no redundant empty lines between methods or code blocks, spaces rather than tabs, etc.
[ ] No Code Analysis warnings
[x] There is proper unit test coverage
[x] If the code is copied from StackOverflow (or a blog or OSS) full disclosure is included. That includes required license files and/or file headers explaining where the code came from with proper attribution
[x] There are very few or no comments (because comments shouldn't be needed if you write clean code)
[x] Xml documentation is added/updated for the addition/change
[x] Your PR is (re)based on top of the latest commits from the main branch (more info below)
[x] Link to the issue(s) you're fixing from your PR description. Use fixes #<the issue number>
[x] Readme is updated if you change an existing feature or add a new one
[ ] Run either build.cmd or build.ps1 and ensure there are no test failures

I'm developing on Linux and can't seem to get the project to build and test, so I'm hoping CI can bail me out.

Humanizr / Humanizer

Change th-TH culture to th #1522