It's essential to most Latvians, possibly (5)
I believe the answer is:
vital
'it's essential' is the definition.
(similar in meaning)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for vital that I've seen before include "Essential to life, indispensable" , "Essential to life or critically important" , "Essential, life-giving" , "Critical, necessary" , "Crucially important, essential" .)