Investing overseas denominated in your own currency doesn't always turn a profit.
Literal
Own-country-currency-denominated [by means of-で] overseas [to-に] invest [nominalizer-こと][subject-が] always profit [object-を] produce [quotative-と][topic-は] is-not-limited.
A financial observation using ~とは限らない 'it's not necessarily the case that.' 自国通貨建て is a specialized compound: 自国 'own country' + 通貨 'currency' + 建て 'denominated in.' The nominalized clause [verb]ことが as subject is standard written register. いつも…とは限らない means 'doesn't always' — the は after と emphasizes the scope of the negation.