Added language selection using command (as alternative to GUI)

Implements https://github.com/BentoBoxWorld/BentoBox/issues/1411
The IslandLanguageCommand now have tab-completion.
Added LocalesManager#isLocaleAvailable(Locale).

src/main/java/world/bentobox/bentobox/api/commands/island/IslandLanguageCommand.java

@@ -1,10 +1,12 @@
 package world.bentobox.bentobox.api.commands.island;
 
-import java.util.List;
+import java.util.*;
 
+import org.bukkit.Bukkit;
 import world.bentobox.bentobox.api.commands.CompositeCommand;
 import world.bentobox.bentobox.api.user.User;
 import world.bentobox.bentobox.panels.LanguagePanel;
+import world.bentobox.bentobox.util.Util;
 
 /**
  * @author Poslovitch
@@ -20,11 +22,40 @@ public class IslandLanguageCommand extends CompositeCommand {
         setPermission("island.language");
         setOnlyPlayer(true);
         setDescription("commands.island.language.description");
+        setParametersHelp("commands.island.language.parameters");
     }
 
     @Override
     public boolean execute(User user, String label, List<String> args) {
-        LanguagePanel.openPanel(user);
+        if (args.size() == 1) {
+            // The user provided a language code
+            Locale locale = Locale.forLanguageTag(args.get(0));
+            if (getPlugin().getLocalesManager().isLocaleAvailable(locale)) {
+                // Check if that locale is not already selected
+                if (!user.getLocale().equals(locale)) {
+                    getPlugin().getPlayers().setLocale(user.getUniqueId(), locale.toLanguageTag());
+                    user.sendMessage("language.edited", "[lang]", locale.toLanguageTag());
+                } else {
+                    user.sendMessage("commands.island.language.already-selected");
+                    return false;
+                }
+            } else {
+                user.sendMessage("commands.island.language.not-available");
+                return false;
+            }
+        } else {
+            LanguagePanel.openPanel(user);
+        }
         return true;
     }
+
+    @Override
+    public Optional<List<String>> tabComplete(User user, String alias, List<String> args) {
+        List<String> options = new ArrayList<>();
+        String lastArg = !args.isEmpty() ? args.get(args.size()-1) : "";
+        for (Locale locale : getPlugin().getLocalesManager().getAvailableLocales(true)) {
+            options.add(locale.toLanguageTag());
+        }
+        return Optional.of(Util.tabLimit(options, lastArg));
+    }
 }

src/main/java/world/bentobox/bentobox/managers/LocalesManager.java

@@ -296,6 +296,16 @@ public class LocalesManager {
         }
     }
 
+    /**
+     * Returns {@code true} if this locale is available, {@code false} otherwise.
+     * @param locale the locale, not null. Consider using {@link Locale#forLanguageTag(String)} if needed.
+     * @return {@code true} if this locale is available, {@code false} otherwise.
+     * @since 1.14.0
+     */
+    public boolean isLocaleAvailable(@NonNull Locale locale) {
+        return languages.containsKey(locale);
+    }
+
     /**
      * @return raw map of system locales to BentoBox locales
      */

src/main/resources/locales/en-US.yml

@@ -657,6 +657,9 @@ commands:
       description: "display island settings"
     language:
       description: "select language"
+      parameters: "[language]"
+      not-available: "&c This language is not available."
+      already-selected: "&c You are already using this language."
     expel:
       description: "expel a player from your island"
       parameters: "<player>"