Trying to answer myself with some cleaning. So, which existing or potential Wikisources lack OCR with FineReader (and Tesseract?) but are interested in Google's, beyond Bengali?
== Languages supported by FineReader, not Google ==
Abkhaz Adyghe Agul Altaic Avar Blackfoot Bugotu Buryat Chamorro Chukchee Corsican Crow Dargwa Dungan Dutch (Belgium) Eskimo (Cyrillic, Latin) Even Evenki Frisian Friulian Gagauz German (Luxemburg) German (old spelling) Hani Ido Ingush Interlingua Jingpo Kabardian Kalmyk Karachay-balkar Kasub Kawa Khakass Khanty Korean (Hangul) Koryak Kpelle Kumyk Kurdish Lak Lezgi Luba Malinke Mansi Mari Maya Miao Moldavian Mordvin Nenets Nivkh Nogay Norwegian (Nynorsk) Occidental Ojibway Ossetian Provencal Rhaeto-romanic Rwanda Sami (Lappish) Selkup Somali Sorbian Sotho Sunda Tabasaran Tagalog Tok Pisin Tun Turkmen (Latin) Tuvinian Udmurt Uighur (Cyrillic, Latin) Ukrainian Yakut
== Languages supported by Google, not FineReader ==
Acehnese Acholi Adangme Akan Algonquinian Amharic Ancient Greek Araucanian/Mapuche Assamese Asturian Athabaskan Balinese Bambara Bantu Batak Bengali Bikol Bislama Bosnian Burmese Cherokee Chinese (Mandarin; Hong Kong) Choctaw Cree Creek Dhivehi Duala Dzonkha Efik Ewe Filipino Fon Fulah Ga Gayo Georgian Gilbertese Gothic Gujarati Haitian Creole Herero Hiligaynon Hindi Iban Igbo Iloko Javanese Kabyle Kachin Kalaallisut Kamba Kannada Kanuri Khasi Khmer Kinyarwanda Komi Kosraean Kuanyama Lao Lingala Low German Lozi Luba-Katanga Luo Madurese Malayalam Mandingo Manx Marathi Marshallese Mende Middle English Middle High German Mongo Navajo Ndonga Nepali Niuean Northern Sotho North Ndebele Nyankole Nyasa Tonga Nzima Ojibwa Old English Old French Old High German Old Norse Old Provencal Oriya Ossetic Pampanga Pangasinan Pashto Persian Punjabi (Gurmukhi) Romansh Sakha Sango Sanskrit Scots Sinhala Songhai Southern Sotho Sundanese Tamil Telugu Temne Tibetan Tigirinya Tsonga Udmurt Ukrainian Urdu Venda Votic Western Frisian Yoruba