feat(languages): add Slovenian 1k and 5k word lists (@anzepintar) (#5889

)

### Description

Added Slovenian 1k and 5k word lists
source is from clarin.si -> ccKUUS (učbeniki za učenje slovenščine)

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### Checks

- [ ] Adding quotes?
- [ ] Make sure to include translations for the quotes in the
description (or another comment) so we can verify their content.
- [x] Adding a language or a theme?
- [x] If is a language, did you edit `_list.json`, `_groups.json` and
add `languages.json`?
  - [ ] If is a theme, did you add the theme.css?
- Also please add a screenshot of the theme, it would be extra awesome
if you do so!
- [x] Check if any open issues are related to this PR; if so, be sure to
tag them below.
- [x] Make sure the PR title follows the Conventional Commits standard.
(https://www.conventionalcommits.org for more info)
- [x] Make sure to include your GitHub username prefixed with @ inside
parentheses at the end of the PR title.

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Closes #

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frontend/static/languages/_groups.json

@@ -198,7 +198,7 @@
   },
   {
     "name": "slovenian",
-    "languages": ["slovenian"]
+    "languages": ["slovenian", "slovenian_1k", "slovenian_5k"]
   },
   {
     "name": "croatian",

frontend/static/languages/_list.json

@@ -125,6 +125,8 @@
   ,"slovak_1k"
   ,"slovak_10k"
   ,"slovenian"
+  ,"slovenian_1k"
+  ,"slovenian_5k"
   ,"croatian"
   ,"dutch"
   ,"dutch_1k"

frontend/static/languages/slovenian.json

@@ -1,5 +1,6 @@
 {
   "name": "slovenian",
+  "bcp47": "sl-SI",
   "words": [
     "hitro",
     "potem",