In just two lines, Abbie describes a moment of connection that arrives almost by accident. The speaker "suddenly" begins speaking "his language," and from then on is "never again misunderstood." The word "suddenly" makes it feel like a switch flipping rather than something learned through effort.
The "language" probably isn't a literal one. Judging by the poem, it could mean a way of listening, a shared emotional understanding, or the speaker finally finding words the other person can hear. The setting matters too: this happens "in the quietness." Understanding seems to come when the noise falls away, not when people argue their case louder.
The mood is calm and quietly relieved. There's a sense of ease, even gratitude, but also a small hint of question. The speaker is the one who changes, adopting his language, so we might wonder what it cost, or whether being understood meant meeting him on his terms. The poem leaves that open.