To keep a day is an idiom that means to celebrate it. AT: "to celebrate the fourteenth and fifteenth days of Adar every year" (See: [[rc://en/ta/man/translate/figs-idiom]])
Turning represents changing. The abstract nouns sorrow and joy can be expressed with "sad" and "joyful." AT: "they changed from being very sad to being joyful" (See: [[rc://en/ta/man/translate/figs-metaphor]])