Learn Hardcore Indonesian: Kami berlatih sekali per hari selama dua minggu.

kami = we/us, excluding the person you’re talking to.
kita = we/us, including the person you’re talking to. So Kami berlatih... means the listener was not part of the training group. If you say Kita berlatih..., you’re including the listener as part of the group.

What does "berlatih" mean exactly? How is it different from "latihan," "melatih," and "berolahraga"?

berlatih = to practice (intransitive, the doer practices a skill). Example: Kami berlatih setiap sore.
latihan = practice/practice session (noun). Colloquially it can act like a verb: Kami latihan setiap sore.
melatih = to train (someone/something) (transitive). Example: Pelatih melatih tim.
berolahraga = to exercise/do sports (general physical exercise). Example: Saya berolahraga setiap hari. You can name the skill after berlatih: Kami berlatih gitar / renang / sepak bola.

Is "sekali per hari" natural? Are there more idiomatic ways to say “once a day”?

Yes, it’s correct. Other very common variants:

sekali sehari (very common, natural)
sehari sekali (also common)
satu kali sehari (explicit “one time”)
sekali per hari (fine, a bit more formal/technical)
setiap hari sekali (grammatical but less common than the first two)

Can the time expressions move around? Where can I place "selama dua minggu" and the “once a day” part?

These are all fine:

Selama dua minggu, kami berlatih sekali sehari.
Kami berlatih sekali sehari selama dua minggu.
Kami berlatih selama dua minggu, sekali sehari. (acceptable for emphasis; less common in everyday speech) Keep the frequency phrase together (e.g., sekali sehari) so it’s easy to parse.

What tense is this? How do I say past, present, or future?

Indonesian verbs don’t inflect for tense. Context or time words mark time:

Past/already: Kami sudah berlatih..., Kami baru saja berlatih...
Habitual/present: Kami berlatih... (context shows it’s a routine)
Future: Kami akan berlatih..., Besok kami berlatih...
In progress now: Kami sedang berlatih.

Any spelling or spacing gotchas with "per hari," "sehari," and "sekali"?

Write per hari as two words (not “perhari” or “per-hari”).
Write sehari as one word (“a day/per day”).
Write sekali as one word (“once”).

Why "selama"? How is it different from "untuk," "dalam," and "sejak"?

selama = for/during a duration: Kami berlatih selama dua minggu.
untuk = for (purpose/intended use). People sometimes use it with time, but selama is the safest for stating duration: Kami akan tinggal di Bali selama dua minggu.
dalam = within/in (deadline/time limit): Selesaikan tugas dalam dua minggu.
sejak = since (starting point): Kami berlatih sejak dua minggu lalu.

Does "minggu" ever mean Sunday? Could "dua minggu" be ambiguous?

Yes, capitalization distinguishes them:

minggu (lowercase) = week. dua minggu = two weeks.
Minggu (capitalized) = Sunday. If you want a synonym for “week,” you can also use pekan: dua pekan.

I’ve seen "dua minggu sekali." Is that the same as this sentence?

No. dua minggu sekali means “once every two weeks” (biweekly). Your sentence means “once a day for two weeks,” e.g. sekali sehari selama dua minggu.

How do I say other frequencies like twice a day or three times a week?

Use “kali” (times) plus the period:

dua kali sehari = twice a day
tiga kali seminggu / seminggu tiga kali = three times a week
dua hari sekali = every other day
sebulan sekali = once a month
beberapa kali sehari = several times a day

Can I drop "kami"?

Yes. Subjects are often omitted when clear from context:

Berlatih sekali sehari selama dua minggu. Use kami if there’s any chance of ambiguity.

Can "berlatih" take an object? Which prepositions go with it?

Often intransitive: Kami berlatih setiap sore.
Can be followed by the activity/skill: Kami berlatih gitar / renang / sepak bola.
Common prepositions:
- Place: di — Kami berlatih di gym.
- Purpose/goal: untuk — Kami berlatih untuk pertandingan.
- With/using: dengan — Kami berlatih dengan pelatih baru.