Split language-specific files

I noticed today that this app is 33.9 MB (or 38 MB, depending on who you ask) installed and was curious why.

```
$ du -h | sort -h | tail -n20
228K ./share/vim/vim81/lang/sr
232K ./share/vim/vim81/lang/ru/LC_MESSAGES
236K ./share/vim/vim81/lang/ru
244K ./lib
268K ./share/vim/vim81/compiler
368K ./share/vim/vim81/keymap
556K ./share/vim/vim81/autoload/xml
864K ./share/vim/vim81/indent
1004K ./share/vim/vim81/ftplugin
2.1M ./share/vim/vim81/autoload
2.3M ./share/vim/vim81/tutor
3.1M ./bin
3.6M ./share/vim/vim81/spell
6.6M ./share/vim/vim81/syntax
7.1M ./share/vim/vim81/lang
7.8M ./share/vim/vim81/doc
33M ./share
33M ./share/vim
33M ./share/vim/vim81
37M .
```

Digging into `share/vim/vim81`:

```
$ du -h share/vim/vim81/ | sort -h | tail -n20
216K share/vim/vim81/pack/dist
220K share/vim/vim81/lang/uk/LC_MESSAGES
220K share/vim/vim81/pack
224K share/vim/vim81/lang/sr/LC_MESSAGES
224K share/vim/vim81/lang/uk
228K share/vim/vim81/lang/sr
232K share/vim/vim81/lang/ru/LC_MESSAGES
236K share/vim/vim81/lang/ru
268K share/vim/vim81/compiler
368K share/vim/vim81/keymap
556K share/vim/vim81/autoload/xml
864K share/vim/vim81/indent
1004K share/vim/vim81/ftplugin
2.1M share/vim/vim81/autoload
2.3M share/vim/vim81/tutor
3.6M share/vim/vim81/spell
6.6M share/vim/vim81/syntax
7.1M share/vim/vim81/lang
7.8M share/vim/vim81/doc
33M share/vim/vim81/
```

`share/vim/vim81/lang` is a funny mix of localized `menu_$LANG.vim` files, and standard gettext-ish per-locale directories in an unusual path. It should be possible to ship `share/vim/vim81/lang` in a Locale extension that can be partially-installed in the normal way.

There are also locale-specific files in `share/vim/vim81/tutor` and `share/vim/vim81/spell`, if one could bring oneself to arrange the necessary symlink farms