summer is kársa

kársa = summer (seasons)
alternate spelling: kahrsa

Some things Google found for "karsa":
Karsa Orlong is a fictional male character in Steven Erikson's fantasy series Malazan Book of the Fallen. Karsa is an unusual last name. Karsa is a rare first name. In Indonesian karsa means intention. Karsa (or K'arsa) is the name of a place in Ethiopia.

Word derivation for "summer" :
Hungarian = nyár
Finnish = kesä
Samgur = kársa

Making this word, I changed the ä to a for vowel harmony.

winter is tali

tali = winter (seasons)

Some things Google found for "tali":
Tali is a uncommon feminine first name which can be Hebrew. Tali is an uncommon to unusual last name. In Latin tali are anklebones or knucklebones. In Finnish tali means tallow. In Malay tali means rope. Tali is the name of places in Finland, Estonia, Sudan, Pakistan and China.

Word derivation for "winter" :
Hungarian = tél
Finnish = talvi
Samgur = tali

autumn is sösk

sösk = autumn (seasons)
alternate spelling: seusk

Some things Google found for "sösk" and "sosk":
SÖSK stands for Sydöstra Skånes Samarbetskommitté (Southeast Skåne Cooperation Committee) of Sweden. Sosk is an rare last name. SOSK design of an Icelandic designer. SOSK is an Australian non-profit for children and women in Kenya. Chamy Sosk is the name of a place in Iraq.

Word derivation for "autumn" :
Hungarian = ősz (which I transliterate to ös)
Finnish = syksy (which I transliterate to süksü)
Samgur = sösk