Open User Defined Language folder:
Copy the tcl2.xml file from the repository to this folder and reload Notepad++:
New syntax highlighting appears in the language menu:
Write your code:
Notepad++ uses XML configuration files to define the per-language function and parameter auto-completion. Those AutoComplete files are located in the autoCompletion subdirectory of the Notepad++ install folder. (In older versions, Notepad++ v7.6.1 and earlier, they were found in the plugins\APIs subdirectory of the intstall folder.)
In my case just copy autoCompletion/tcl.xml
to C:\Program Files\Notepad++\autoCompletion\
and functionList/tcl.xml
to C:\Program Files\Notepad++\functionList\
Reboot Notepad++
Enjoy