In western schools is a tradition to use Greek letters to denote angles. I wonder what about Greek schools do they also use Greek letters to denote angles or do they prefer other kind of alphabet to avoid confusion?
An answer to both question and first comment:
Usually, numbers or the letters phi, omega are selected to denote angles, while x and y are the standard symbols for independent and dependent variables in functions.
See for example the 10th grade (15 years old) geometry book: http://ebooks.edu.gr/ebooks/v/pdf/8547/2608/22-0236-01_Eukleideia-Geometria_A-Lykeiou_Vivlio-Mathiti/ Theorem 1 at page 26,
The Algebra book of the same grade at http://ebooks.edu.gr/ebooks/v/pdf/8547/2466/22-0270-01_Algebra-kai-Stoicheia-Pithanotiton_A-Lykeiou_Vivlio-Mathiti/ Definition at page 146.