"high risk" is a correct and usable phrase in written English. You can use it in any context to describe a situation that carries a greater chance of an undesirable outcome. For example, "Investing in the stock market can be a high risk endeavor.".
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union