Galard is the universal language of interstellar trade and commerce, used by various races throughout the galaxy. The Yeerk Empire uses this language extensively in order for the Gedd, Taxxon, Hork-Bajir and Horse-Controllers to communicate with one another.
"It was Galard, the new language we had learned from the Ongachic hosts. It is the common inter-galactic language. The Yeerk language was impossible to speak with Gedd mouths. Even Galard came out distorted."
"He'd been speaking Galard so far — the language of interstellar trade and commerce. It was the language many races had learned, back when the galaxy was at peace. It was used to communicate between different species."