<p>Whoa, interesting! When I tested the API, it seemed Mapzen supports the localization correctly now.</p>

<p>However, per <a href="https://mapzen.com/documentation/turn-by-turn/api-reference/#directions-options">their API documentation</a>, you should pass e.g. <code>cs-CZ</code> instead of <code>cs</code> (which is what <code>I18n.currentLocale()</code> returns, IIANM). In the latter case, the default en-US localization is used. And this is what I am seeing when testing it now live, so, IIANM, the remapping would be required anyway (also, cf. <a href="https://github.com/openstreetmap/openstreetmap-website/blob/master/app/assets/javascripts/index/directions/mapquest.js#L45"><code>mapquest.js</code></a>).</p>

<p>Check for yourself: <a href="https://valhalla.mapzen.com/route?api_key=valhalla-7UikjOk&json=%7B%22locations%22%3A%5B%7B%22lat%22%3A50.1055%2C%22lon%22%3A14.568%7D%2C%7B%22lat%22%3A50.1016%2C%22lon%22%3A14.5563%7D%5D%2C%22costing%22%3A%22auto%22%2C%22directions_options%22%3A%7B%22units%22%3A%22km%22%2C%22language%22%3A%22cs%22%7D%7D"><code>cs</code></a>, <a href="https://valhalla.mapzen.com/route?api_key=valhalla-7UikjOk&json=%7B%22locations%22%3A%5B%7B%22lat%22%3A50.1055%2C%22lon%22%3A14.568%7D%2C%7B%22lat%22%3A50.1016%2C%22lon%22%3A14.5563%7D%5D%2C%22costing%22%3A%22auto%22%2C%22directions_options%22%3A%7B%22units%22%3A%22km%22%2C%22language%22%3A%22cs-CZ%22%7D%7D"><code>cs-CZ</code></a></p>

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