Add Japanese language files

Another new language! And this is a very interesting one, since it's
based on Nicalis' translation for 3DS and Switch (with their go-ahead).
Which means I had to convert between two completely different
language file formats, which was some work, but it's totally worth it!

Naturally, there are a lot of missing strings, so a translator will
still need to fill in all the blanks (and maintain the translation for
new strings of course)

desktop_version/lang/ja/meta.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<langmeta>
+    <active>1</active>
+
+    <!-- should be lowercase because menu style, and should be in the language itself -->
+    <nativename>日本語</nativename>
+
+    <!-- English translation by X -->
+    <credit>Converted from Nicalis version</credit>
+
+    <!-- On the language screen, hard limit 40 8x8 characters. Space/Z/V sets this as the language -->
+    <action_hint>Press Space, Z, or V to select</action_hint>
+
+    <!-- Same as above, but for a gamepad button (hard limit 40 8x8 characters) -->
+    <gamepad_hint>Press {button} to select</gamepad_hint>
+
+    <!-- Enable automatic word wrapping instead of having to manually insert newlines -->
+    <autowordwrap>0</autowordwrap>
+
+    <!-- Enable automatic full-caps display of selected menu options ([SELECTED] not selected) -->
+    <toupper>0</toupper>
+
+    <!-- When automatically uppercasing, map i to İ (for Turkish) -->
+    <toupper_i_dot>0</toupper_i_dot>
+
+    <!-- When automatically uppercasing, allow ~ to be used to stop the next letter from being uppercased (for Irish) -->
+    <toupper_lower_escape_char>0</toupper_lower_escape_char>
+
+    <!-- The indication that a certain menu option or button is selected -->
+    <menu_select>[ {label} ]</menu_select>
+    <menu_select_tight>[{label}]</menu_select_tight>
+
+    <!-- The filename of the font to use. For example, "font_cn" means font_cn.png and font_cn.fontmeta. -->
+    <font>font_ja</font>
+</langmeta>