Code-Switching is the linguistic phenomenon where a speaker alternates between two or more languages within a single conversation or sentence ("I want to go to the plage because il fait beau") — a common feature of multilingual communication that poses challenges and opportunities for NLP.

NLP Context

• Data: Code-switched text is valuable for multilingual pre-training because it acts as a natural bridge between languages.
• Challenge: Monolingual models fail completely on code-switched text.
• Synthetic: Can generate synthetic code-switched data (randomly translating words) to improve multilingual alignment (Code-Switched Pre-training).

Why It Matters

• Social Media: Hinglish (Hindi-English), Spanglish (Spanish-English) are dominant on social platforms.
• Verification: Tests if a model truly shares a semantic space (can it handle "The [dog] aboyé")?
• Alignment: Synthetic code-switching is a powerful data augmentation technique for cross-lingual transfer.

Code-Switching is mixed-language speech — natural or synthetic mixing of languages that serves as a bridge for aligning multilingual models.