Add optional internationalization support

honey-common/src/dev/shiza/honey/message/key/MessageKeyProcessingException.java

@@ -0,0 +1,14 @@
+package dev.shiza.honey.message.key;
+
+import java.util.Locale;
+
+public final class MessageKeyProcessingException extends IllegalArgumentException {
+
+  public MessageKeyProcessingException(final Locale locale) {
+    super("Could not resolve message for language with tag %s.".formatted(locale));
+  }
+
+  public MessageKeyProcessingException(final String key) {
+    super("Could not resolve message with key %s.".formatted(key));
+  }
+}

honey-common/src/dev/shiza/honey/message/key/MessageKeyProcessor.java

@@ -0,0 +1,27 @@
+package dev.shiza.honey.message.key;
+
+import dev.shiza.honey.processor.Processor;
+import java.util.Locale;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public final class MessageKeyProcessor implements Processor {
+
+  private static final Pattern MESSAGE_PATTERN = Pattern.compile("\\[\\[(\\w+):([^]]+)]]");
+  private final MessageSource messageSource;
+
+  public MessageKeyProcessor(final MessageSource messageSource) {
+    this.messageSource = messageSource;
+  }
+
+  @Override
+  public String process(final String content) {
+    final Matcher matcher = MESSAGE_PATTERN.matcher(content);
+    if (matcher.find()) {
+      final Locale locale = Locale.forLanguageTag(matcher.group(1));
+      final String key = matcher.group(2);
+      return messageSource.message(locale, key);
+    }
+    return content;
+  }
+}

honey-common/src/dev/shiza/honey/message/key/MessageSource.java

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+package dev.shiza.honey.message.key;
+
+import java.util.Locale;
+import java.util.Map;
+
+public interface MessageSource {
+
+  void register(final Locale locale, final Map<String, String> messages);
+
+  String message(final Locale locale, final String key);
+}