run textcomponenttranslations through the ForgeI18N message format translator as well.

src/main/java/net/minecraftforge/fml/TextComponentMessageFormatHandler.java

@@ -0,0 +1,18 @@
+package net.minecraftforge.fml;
+
+import net.minecraft.util.text.ITextComponent;
+import net.minecraft.util.text.TextComponentString;
+import net.minecraft.util.text.TextComponentTranslation;
+
+import java.util.List;
+
+public class TextComponentMessageFormatHandler {
+    public static int handle(final TextComponentTranslation parent, final List<ITextComponent> children, final Object[] formatArgs, final String format) {
+        try {
+            children.add(new TextComponentString(ForgeI18n.parseFormat(format, formatArgs)));
+            return format.length();
+        } catch (IllegalArgumentException ex) {
+            return 0;
+        }
+    }
+}