Update i18n overview in the manual.

Remove obsolete warning about gettext 0.10, add a link to Poedit instead.

Also fix Doxygen markup: @see can't be used inside a list item.

See #16714.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78257 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Update wxGetTranslation() documentation.

Document "i18n" trace mask.

Correct warning about [not] using wxT().

See #16714.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78258 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775