Implement i18nHelper mapped placeholder

 - Document i18nHelper placeholder

Helpers.md

@@ -125,6 +125,24 @@ Provides messages for a given key, translated using the locale of the content no
 ```handlebars
 {{{t 'web.patterns.paging.next'}}}
 ```
+#### placeholders
+messages can contain either indexed or mapped placeholders.
+##### indexed
+```properties
+web.patterns.paging.current=current page is {0}
+```
+```handlebars
+{{{t 'web.patterns.paging.current' 2}}}
+```
+--> =current page is 2
+##### map
+```properties
+web.patterns.paging.current=current page is {currentPagePlaceholder}
+```
+```handlebars
+{{{t 'web.patterns.paging.current' currentPagePlaceholder=2}}}
+```
+--> =current page is 2
 
 ### [If condition](light-development/src/main/java/com/merkle/oss/magnolia/renderer/handlebars/helpers/IfConditionHelper.java)
 Conditionally renders a block or returns evaluated condition.

light-development/src/main/java/com/merkle/oss/magnolia/renderer/handlebars/helpers/I18nHelper.java

@@ -1,19 +1,22 @@
 package com.merkle.oss.magnolia.renderer.handlebars.helpers;
 
-import com.github.jknack.handlebars.Handlebars;
-import com.github.jknack.handlebars.Options;
-import com.merkle.oss.magnolia.renderer.handlebars.utils.LocaleProvider;
 import info.magnolia.i18nsystem.FixedLocaleProvider;
 import info.magnolia.i18nsystem.SimpleTranslator;
 import info.magnolia.i18nsystem.TranslationService;
 import info.magnolia.jcr.util.ContentMap;
 
-import javax.inject.Inject;
-import javax.jcr.Node;
-import java.io.IOException;
 import java.util.Locale;
 import java.util.Set;
 
+import javax.inject.Inject;
+import javax.jcr.Node;
+
+import org.apache.commons.text.StringSubstitutor;
+
+import com.github.jknack.handlebars.Handlebars;
+import com.github.jknack.handlebars.Options;
+import com.merkle.oss.magnolia.renderer.handlebars.utils.LocaleProvider;
+
 public class I18nHelper implements NamedHelper<String> {
 	private final TranslationService translationService;
 	private final LocaleProvider localeProvider;
@@ -32,7 +35,7 @@ public CharSequence apply(final String key, final Options options) {
 		final Node node = ((ContentMap) options.get("content")).getJCRNode();
 		final Locale locale = localeProvider.getLocale(node);
 		final SimpleTranslator simpleTranslator = new SimpleTranslator(translationService, new FixedLocaleProvider(locale));
-		final String message = simpleTranslator.translate(key, options.params);
+		final String message = new StringSubstitutor(options.hash, "{", "}").replace(simpleTranslator.translate(key, options.params));
 		return new Handlebars.SafeString(message);
 	}