/HS18*50:18*14@0:GDI32.dll:GetTextMetricsA
The H-code works with AGTH, ITH and Textractor.
ITHVNR and VNR can’t use it as is, but there’s a workaround: attach ITH to the game, use the H-code above, then select it in ITH’s hook editor and click Generate Code button. The converted H-code (for example, /HS18*50:18*14@1D1DA:gdi32.dll) will work in ITHVNR and VNR, but it will be bound to your specific version of gdi32.dll and may not work in other versions of Windows.
Also, if you want to use ITH, remove ITH’s default hook for ShiinaRio IMMEDIATELY (!) after attaching ITH to the game because when the game window regains focus, the engine will detect ITH’s default hook and will respond by killing itself. That’s why we have to hook system DLL instead of the game engine directly.
P.S. If you're on Windows 7, you can try this really, really old version of ITH (1.6, also attached below for the posterity):
http://s000.tinyupload.com/index.php?file_id=01504152821935649940
This particular version doesn't need any H-codes for this engine, but I don't think that it works in anything newer than Windows 7.
By the way, if ITH 1.6 works for you, it will work with other ShiinaRio games, most notably onomatope*raspberry titles.