[MM-33112] Add support for multiple custom spellchecking languages (#1743)

* [MM-33112] Add support for multiple custom spellchecking languages

* Styles and other formatting

* Type and lint fixes

* Update wording

package.json

@@ -73,6 +73,7 @@
     "@types/react": "^17.0.11",
     "@types/react-beautiful-dnd": "^13.0.0",
     "@types/react-dom": "^17.0.8",
+    "@types/react-select": "^4.0.17",
     "@types/underscore": "^1.11.2",
     "@types/valid-url": "^1.0.3",
     "@types/winreg": "^1.2.30",
@@ -138,6 +139,7 @@
     "react-beautiful-dnd": "^13.1.0",
     "react-bootstrap": "^1.6.1",
     "react-dom": "^16.14.0",
+    "react-select": "4.3.1",
     "react-transition-group": "^2.5.0",
     "sass": "^1.35.1",
     "semver": "^5.5.0",