Modern Text-To-Speech (TTS) systems need to increasingly deal with multilingual input. Navigation, social and news are all domains with a large proportion of foreign words. However, when typical monolingual TTS voices are used, the synthesis quality on such input is markedly lower. This is because traditional TTS derives pronunciations from a lexicon or a Grapheme-To-Phoneme (G2P) model which was built using a pre-defined sound inventory and a phonotactic grammar for one language only. G2P models perform poorly on foreign words, while manual lexicon development is labour-intensive, expensive and requires extra storage. Furthermore, large phoneme inventories and phonotactic grammars contribute to data sparsity in unit selection systems. We present an automatic system for deriving pronunciations for foreign words that utilises the monolingual voice design and can rapidly scale to many languages. The proposed system, based on a neural network cross-lingual G2P model, does not increase the size of the voice database, doesn't require large data annotation efforts, is designed not to increase data sparsity in the voice, and can be sized to suit embedded applications.