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Allan, the Google resource is the base. However, remember always that: Google suggests using always the rel="canonical", even if it's only self-referential. The href in the hreflang must always indicate a canonical URL. If not, Google will consider it a mistake and won't consider the hreflang. If you're targeting two different languages (i.e.: English and Spanish), the use of the hreflang is not strictly necessary, however using it is another signal you give to Google about how you want your urls target a specific audience based on language or language/country.