A good app to play with relays is Nostrrr: https://nostrrr.com/relay/nrelay1qq08wumn8ghj7en9v4j8xtnwdaehgu3wvfskuep0d3skuee0dfssy3jex8

You can also try sending custom filters to relay.nostr.band like {"kinds":[1],"@lang":["de","ja"]} - there is no NIP for this, but if there is some demand for such stuff we could come up with one.

The detector is CLD2 which isn't too accurate, but extremely fast.

Supported languages and their codes:

AFRIKAANS af

ALBANIAN sq

ARABIC ar

AZERBAIJANI az

BASQUE eu

BELARUSIAN be

BENGALI bn

BIHARI bh

BOSNIAN bs

BULGARIAN bg

CATALAN ca

CEBUANO ceb

CROATIAN hr

CZECH cs

Chinese zh

ChineseT zh-Hant

DANISH da

DUTCH nl

ENGLISH en

ESTONIAN et

FINNISH fi

FRENCH fr

GALICIAN gl

GANDA lg

GERMAN de

GREEK el

HAITIAN_CREOLE ht

HAUSA ha

HEBREW iw

HINDI hi

HMONG hmn

HUNGARIAN hu

ICELANDIC is

IGBO ig

INDONESIAN id

IRISH ga

ITALIAN it

JAVANESE jw

Japanese ja

KINYARWANDA rw

Korean ko

LATVIAN lv

LITHUANIAN lt

MACEDONIAN mk

MALAY ms

MALTESE mt

MARATHI mr

NEPALI ne

NORWEGIAN no

PERSIAN fa

POLISH pl

PORTUGUESE pt

ROMANIAN ro

ROMANIAN ro

RUSSIAN ru

SCOTS_GAELIC gd

SERBIAN sr

SERBIAN sr

SLOVAK sk

SLOVENIAN sl

SOMALI so

SPANISH es

SWAHILI sw

SWEDISH sv

TAGALOG tl

THAI th

TURKISH tr

UKRAINIAN uk

URDU ur

VIETNAMESE vi

WELSH cy

YIDDISH yi

YORUBA yo

ZULU zu