As far as I know, both in Russian and in English, there was a separate tense for such conditional sentences.
In English, it eventually merged with the past (but the verb to be — it retained a separate form in singular: ‘I were’ vs ‘I was’).
In Russian, modern past verbs ending with -л are actually participles (that’s why they don’t conjugate and do have gender) which formerly (before the loss of obligatory copula быть) were constructions ‘быть(pres.) + participle’. In conditional, ‘быть(cond) + participle’ turned into modern ‘бы + глагол на -л’.