Pull Request for Issue #38077 .

Summary of Changes

• Add language string JLIB_INSTALLER_ERROR_DOWNLOAD_SERVER_CONNECT taken from the "lib_joomla.ini" language file to the installation language file. This is what has been done before with PR #37286 for other languages strings from the library which were not translated in the installation.
• The installer's languages model should not use language string COM_INSTALLER_MSG_INSTALL_INVALID_URL from "com_installer.ini". Therefore add a new sting INSTL_ERROR_INVALID_URL to the installation language file and use that string instead of the one from the component in the model.

Testing Instructions

It's very likely that you can't reproduce the errors mentioned in the description of issue #38077 to cause the untranslated string being shown, so we might be limited to code review here.

But if you can reproduce it, then please do a real test and report back how you have tested.

Actual result BEFORE applying this Pull Request

Untranslated strings mentioned in the issue are shown in certain case of error.

Expected result AFTER applying this Pull Request

The strings are translated in this particular case of error.

Documentation Changes Required

None.