Direct answer: It doesn’t have a literal meaning — the English equivalent is simply “tra‑la‑la” or “la‑la‑la” (nonsensical singing syllables).
Explanation
- “Tralalero tralala” (or variants like “tra‑la‑le‑ro, tra‑la‑la”) are vocalise or vocables used in songs — filler syllables to indicate singing, merriment, or to carry a melody.
- There’s no real-word translation; in English you’d usually render it as “tra‑la‑la,” “la‑la‑la,” or leave it unchanged in lyrics.
Example: She skipped along, singing “tra‑la‑la” (i.e., singing happily).