You can use SpeechRecognitionEngine (CultureInfo) overload.
var speechRec = new SpeechRecognitionEngine(new CultureInfo("es-ES")));
This assumes that the user has set up a Spanish culture, otherwise an ArgumentException will be thrown. The SpeechRecognitionEngine class implements IDisposable , so it is recommended that you call speechRec.Dispose() when you're done, or use it in a using statement.
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