彼女は日記をつけることに決めた。

she; her; her; girlfriend; sweetheart

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

diary; journal

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to turn on; to switch on; to light up

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

to decide; to choose; to determine; to make up one's mind; to resolve; to set one's heart on; to settle; to arrange; to set; to appoint; to fix; to clinch (a victory); to decide (the outcome of a match); to persist in doing; to go through with; to always do; to have made a habit of; to take for granted; to assume; to dress up; to dress to kill; to dress to the nines; to carry out successfully (a move in sports, a pose in dance, etc.); to succeed in doing; to immobilize with a double-arm lock (in sumo, judo, etc.); to eat or drink something; to take illegal drugs