title: Set locale to cartopy ticker
body: <p>I was wondering and searching on the docs: is there a way to set the locale, for example, to use commas instead of points as separators for decimals in cartopy ticklabels?</p>
  
  <p>In matplotlib it can be done, but it doesn't apply to cartopy.mpl.ticker's LongitudeFormatter and LatitudeFormatter.</p>
  
  <p>Maybe it's something for the developers to add in newer versions?</p>