Þegar afmælisbarnið kemur, segjum við: „Til hamingju!“

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Breakdown of Þegar afmælisbarnið kemur, segjum við: „Til hamingju!“

• segja: to say
• þegar: when
• koma: to arrive

Questions & Answers about Þegar afmælisbarnið kemur, segjum við: „Til hamingju!“

What does Þegar mean here, and does it change the grammar of the clause that follows?

Þegar means when (sometimes closer to whenever/once depending on context). It introduces a subordinate (dependent) clause: Þegar afmælisbarnið kemur.
In Icelandic, subordinate clauses typically keep normal subject–verb order (subject before verb), which is exactly what you see: afmælisbarnið (subject) + kemur (verb).

Why is there a comma after kemur?

It’s the standard punctuation rule: when a subordinate clause (introduced by þegar, ef, því að, etc.) comes first, it’s usually followed by a comma before the main clause.
So: Þegar … kemur, segjum við …

Why does the main clause say segjum við instead of við segjum?

Because Icelandic follows a verb-second (V2) pattern in main clauses: the finite verb tends to be the second “unit” in the sentence.
When you start the sentence with an adverbial/subordinate clause (Þegar afmælisbarnið kemur), that whole part counts as the first unit, so the verb comes next:

• Þegar afmælisbarnið kemur, segjum við …
  If the sentence began directly with the subject, you’d get:
• Við segjum: …