How can I fetch token from specific Localization Table programatically through extension SDK in twx?

You can call against the table directly.

So within Thingworx it would be LocalizationTables["es"].GetToken{params}

sorry not sure how that would translate into the SDK

I don't think there is a service that allows you to do that by doing a call that specifies the actual localization table you want it from.

The Java code should look like this:

LocalizationTable esLocalizationTable = (LocalizationTable)EntityUtilities.findEntity("es", RelationshipTypes.ThingworxRelationshipTypes.LocalizationTable);
try {
  String valueToken = esLocalizationTable.GetToken("yourtoken");
} catch (Exception e1) {
   e1.printStackTrace();
}