Snerk is by the way also that thin layer you get on top of cooling sauces, soups etc. Thus, I always get disgusted by soups (etc) that have gotten this layer because of the connotations this brings me.
Medical English: rheum /ˈɹum/ (GA)
North American English: crust, sleep, eye-boogers, sand, (eye)gook
Dutch: slaapkorrels ("sleep grains") / slaapkorreltjes (with diminutive), slaapzand ("sleep sand")
German: Schlaf in den Augen ("sleep in the eyes") / Schlafsand ("sleep sand") / Schlafkörnchen ("little sleep grains"), (Schlaf)mätzchen, Schlafdreck ("sleep filth")
Swedish: morgongrus ("morning greeting"), godmorgon/gomorron ("goodmorning"), sömn ("sleep")
Icelandic: stírur
Faroese: svøvnur (m) í eygunum, vágur (m)
Norwegian(Bm): snerk (m)
Norwegian(Nn): snerk(e) (m)Catalan: lleganya
Spaniard Spanish: legaña
Salvadorian Spanish: chelito
European Portuguese: ramelas
Brazilian Portuguese: remela
French: chassie
Italian:cispa
Irish: brach ("pus")
Welsh: môl
Latvian: miegs ("sleep"), miedziņi ("sleepies")
Modern Greek: τσίμπλα tsímpla
Persian: ریم چشم rim-e cheshm ("rheum/gum of the eye"), ژفک zhafk (same), قی چسم qey-e cheshm ("emesis of the eye")
Finnish: rääppä, rähmä, unirähmä, unihiekka
Hungarian: csipa
Northern Sami: siedja, ruddi
Turkish: çapak
Japanese: 目糞 mekuso ("eye-shit")
Korean: 눈곱/눈꼽 nunkkop ("eye-gunk")
Chinese: 眼屎 yánshǐ ("eye shit")
(White) Hmong: quav muag ("shit [of the] eye")
Thai: ขี้ตา khîi taa ("shit [of the] eye"]
Tagalog: muta
Hawai'ian: [maka] piapia ("[eye] starchies")
Esperanto: dormgranoloj ("sleep grains") / okulgranoloj ("eye grains")