Possible Clues:

• What a bilingual speaker may do in different situations ... or a three-part theme hint
• Say "See you mañana," e.g. ... and a hint to each set of circles
• Say 'See you mañana,' e.g. ... and a hint to each set of circles
• Shift between dialects in conversations ... or a three-piece hint to the substitutions in this puzzle's 15th row?
• Shift from one dialect to another, depending on the social context