Difficulty translation key (#1959)

Move the key to name mapping for difficulties into the translation
system.

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

src/client/SinglePlayerModal.ts

@@ -16,11 +16,6 @@ import {
 import { UserSettings } from "../core/game/UserSettings";
 import { TeamCountConfig } from "../core/Schemas";
 import { generateID } from "../core/Util";
-import "./components/baseComponents/Button";
-import "./components/baseComponents/Modal";
-import "./components/Difficulties";
-import { DifficultyDescription } from "./components/Difficulties";
-import "./components/Maps";
 import { getCosmetics } from "./Cosmetics";
 import { FlagInput } from "./FlagInput";
 import { JoinLobbyEvent } from "./Main";
@@ -150,9 +145,7 @@ export class SinglePlayerModal extends LitElement {
                         .difficultyKey=${key}
                       ></difficulty-display>
                       <p class="option-card-title">
-                        ${translateText(
-                          `difficulty.${DifficultyDescription[key as keyof typeof DifficultyDescription]}`,
-                        )}
+                        ${translateText(`difficulty.${key}`)}
                       </p>
                     </div>
                   `,