The official language of Ecuador (and therefore Galapagos) is Spanish. However, English is widely spoken and understood at hotels, restaurants and tourist shops. You will find that almost everyone involved in hosting you during your Galapatours cruise speaks English, and you will be able to ask questions about the islands and their wildlife without any problem.
However, not all crewmembers on Galapatours cruises speak fluent English. We do make sure that our naturalist guides and our hospitality managers have excellent English, but we believe in supporting the local economy and reducing the impact of immigration on the islands. This means that where possible we prefer boat operators that hire local residents.
As with all overseas travel, if you try and speak a few words of the local language now and again then your efforts will be well-received. Taking simple Spanish phrasebook with you, or using an electronic translator on your smart device, is a worthwhile addition to your luggage. If you do rely on some form of electronic translation then do make sure you download any required language packs before you arrive in Galapagos, as internet access can be difficult to find on the archipelago!