What challenges are there in building TTS for non-English languages?

Building text-to-speech (TTS) systems for non-English languages presents several challenges, primarily due to data scarcity, linguistic complexity, and cultural nuances. These challenges require tailored solutions to ensure natural-sounding speech output, which can be difficult to achieve without sufficient resources or understanding of the language’s unique features.

First, data availability is a major hurdle. High-quality TTS systems require large datasets of recorded speech paired with corresponding text. For many non-English languages, such datasets are either limited or nonexistent. For example, languages like Icelandic or Swahili lack the extensive, diverse audio-text corpora available for English. Even when datasets exist, they might not cover regional dialects or speaking styles, leading to models that sound robotic or fail to generalize. Additionally, recruiting native speakers for recording sessions can be costly and time-consuming, especially for languages with smaller speaker populations. Without enough data, models may struggle with pronunciation, intonation, or handling rare words, limiting their practicality.

Second, linguistic differences complicate model design. Non-English languages often have phonetic, grammatical, or tonal features that English-centric models aren’t built to handle. For instance, Mandarin Chinese relies on tonal variations to distinguish word meanings—a feature absent in English. TTS systems must accurately reproduce these tones, which requires specialized training data and acoustic modeling. Similarly, Arabic’s complex morphology, where words are built from root consonants and vowel patterns, poses challenges in text normalization and pronunciation prediction. Agglutinative languages like Turkish or Finnish, which form words by adding multiple suffixes, require models to handle long, context-dependent phonetic sequences. These features demand adjustments to tokenization, prosody modeling, and even the architecture of neural networks used in TTS pipelines.

Finally, computational and cultural considerations add layers of complexity. Many non-English languages are spoken in regions with limited access to high-performance computing infrastructure, necessitating lightweight models that can run on low-resource devices. Additionally, cultural expectations around speech styles—such as formal versus informal address in Japanese or gender-specific intonation patterns in some South Asian languages—require careful handling to avoid unintended offense. For example, a TTS system for Hindi might need to adapt its output based on the listener’s age or social status, which isn’t typically a concern in English. Addressing these issues requires collaboration with native speakers and linguists to ensure both technical accuracy and cultural appropriateness, further increasing development time and cost.