runtime(lang): Revise Makefile (#13589)

* Revise runtime/lang/Makefile
* Use predefined variables (`$@`, `$<`) instead of the actual file names.
  (Adding new rules should become easier.)
* Adjust spacing.
* Regenerate converted menu files

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/lang/menu_tr_tr.iso_8859-9.vim b/runtime/lang/menu_tr_tr.iso_8859-9.vim
index 2c6cbd3..1653e34 100644
--- a/runtime/lang/menu_tr_tr.iso_8859-9.vim
+++ b/runtime/lang/menu_tr_tr.iso_8859-9.vim
@@ -9,7 +9,7 @@
 let did_menu_trans = 1
 let s:keepcpo= &cpo
 set cpo&vim
-scriptencoding iso8859-9
+scriptencoding iso-8859-9
 
 " Top
 menutrans &File	&Dosya