Japanese companies (tend to) have parties that mark particular times of the fiscal year, like Christmas, the end of the year and the new year.
Japanese companies like to have parties to celebrate particular annual occasions like Christmas, the end of the year and the new year.
Japanese companies like to celebrate critical times of the year with Christmas parties, year-end parties and New Year's parties.
「節目の日」は、particular times of the fiscal year; particular annual occasions/events; critical times of the year; special occasions などと表現できます。
英訳１や２で使われている、like Christmas, the end of the year ...のlikeは、「・・・のような、例えば・・・」という意味です。
It's the custom at Japanese companies to have parties to mark turning points or big events in people's lives.
この場合、次のような言い方ができますよ。
ーIt's the custom at Japanese companies to have parties to mark turning points or big events in people's lives.
「日本の会社で節目にパーティーをするのは習慣です」
ここの「節目」は turning points or big events in people's lives のように言えると思います。
ご参考まで！
アメリカ合衆国 
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