As written, the ghouls and ghast created by Ghoul Army are under no obligation to do anything other than obey your spoken commands. If you don't give them any spoken commands they can understand, they will revert to doing what ghouls usually do when not beholden to someone else, i.e.: snack on any tasty flesh nearby and find a crypt to hide out in. Since your character is likely made of tasty flesh, casting this spell without the ability to speak to them is likely to backfire. (While many summoning spells do grant that the summoned creatures are compelled not to attack their summoner, Ghoul Army is not a summoning spell, but a necromancy one.)

Theoretically, yes, you could use Share Language Communal to speak with them. However, note that the spell requires you to touch your targets and allows a will save; The ghouls can (and likely will) resist your casting an unidentified spell on them, especially if they're thinking of eating you.

Many spells that produce minions include text that specifies what the critters do if not specifically commanded otherwise. Summon Monster I, for example, says that creatures not otherwise commanded will attack the caster's enemies to the best of their ability. Ghoul Army has no such text.

As a result, the ghouls and ghast created by Ghoul Army are under no obligation to do anything other than obey your spoken commands. If you don't give your ghouls spoken commands they can understand, they will revert to doing what ghouls usually do when not beholden to someone else, i.e.: snack on any tasty flesh nearby and find a crypt to hide out in. Since your character is likely made of tasty flesh, casting this spell without the ability to speak to them is likely to backfire.

Theoretically, yes, you could use Share Language Communal to speak with them. However, note that the spell requires you to touch your targets and allows a will save; The ghouls can (and likely will) resist your casting an unidentified spell on them, especially if they're thinking of eating you.