Tatoeba's policies for language icons
The image must be easily recognizable by the native speakers of the language. If we show the image to a native speaker and they have no idea which language is represented by the image, it is not a valid image.
The image does not need to be a country flag. Most of our icons are based on country flags because languages are most easily associated to country flags. But if your language can be represented by something else than a flag, it is completely okay.
The image should remain politically correct. For instance it should not contain sexual or offensive visuals. We keep the right to refuse to use the image you suggested if we consider it is inappropriate.
Please take into consideration that the size of our language icons is 30x20 pixels. This is quite small and therefore you should choose an image that can be recognizable at this scale.