Update language preference in preferences when upgrading

The language codes were all renamed, so they have to change in the .cfg file of the user as well.

Contributes to issue CURA-4263.

plugins/VersionUpgrade/VersionUpgrade27to30/VersionUpgrade27to30.py

@@ -9,6 +9,23 @@ from UM.VersionUpgrade import VersionUpgrade #We're inheriting from this.
 _renamed_themes = {
     "cura": "cura-light"
 }
+_renamed_i18n = {
+    "7s": "en_7S",
+    "de": "de_DE",
+    "en": "en_US",
+    "es": "es_ES",
+    "fi": "fi_FI",
+    "fr": "fr_FR",
+    "hu": "hu_HU",
+    "it": "it_IT",
+    "jp": "ja_JP",
+    "ko": "ko_KR",
+    "nl": "nl_NL",
+    "pl": "pl_PL",
+    "ptbr": "pt_BR",
+    "ru": "ru_RU",
+    "tr": "tr_TR"
+}
 
 class VersionUpgrade27to30(VersionUpgrade):
     ##  Gets the version number from a CFG file in Uranium's 2.7 format.
@@ -50,6 +67,11 @@ class VersionUpgrade27to30(VersionUpgrade):
             if parser["general"]["theme"] in _renamed_themes:
                 parser["general"]["theme"] = _renamed_themes[parser["general"]["theme"]]
 
+        #Renamed languages.
+        if "language" in parser["general"]:
+            if parser["general"]["language"] in _renamed_i18n:
+                parser["general"]["language"] = _renamed_i18n[parser["general"]["language"]]
+
         # Re-serialise the file.
         output = io.StringIO()
         parser.write(output)