OCR fails when a requested language does not load.

Tesseract initialises with the languages it can load and drops the
rest; a page asked for in eng+chi_sim was read in English alone and
reported as a success (Ely OCR).

--- a/source/fitz/tessocr.cpp	2026-10-06 16:20:56
+++ b/source/fitz/tessocr.cpp	2026-10-06 16:20:56
@@ -144,6 +144,20 @@
 		delete api;
 		fz_clear_leptonica_mem(ctx);
 		fz_throw(ctx, FZ_ERROR_LIBRARY, "Tesseract language initialisation failed");
+	}
+
+	{
+		std::vector<std::string> loaded;
+		int wanted = 1;
+		for (const char *s = language; *s; s++)
+			wanted += *s == '+';
+		api->GetLoadedLanguagesAsVector(&loaded);
+		if ((int)loaded.size() < wanted)
+		{
+			delete api;
+			fz_clear_leptonica_mem(ctx);
+			fz_throw(ctx, FZ_ERROR_LIBRARY, "Tesseract loaded %d of %d languages in %s", (int)loaded.size(), wanted, language);
+		}
 	}
 
 	n = fz_count_options(ctx, options);