Alejandro is probably treating William unfairly.
Excluding William from any personal discussions or fun throughout the workday by speaking Spanish may not be harassment in terms of a "hostile" work
environment, but it is certainly excluding him that could be considered unfair. And since William is complaining about missing important work information, Alejandro needs to be more careful.
At the very least, Alejandro should make sure that all work discussions take place in English so all of the workers can get the information. And, even though the workers may lapse into Spanish as they talk among themselves,
Alejandro could make more of an effort to translate or ask the others to "let William in" on their jokes as a way of treating William with respect.