I worked as salaried employee in a country that signed a convention with Israel, and insurance contributions were deducted for the Social Security Institute of that country. Are those insurance contributions paid in that country completely lost?

You can submit a claim for old-age pension from the convention country, close to the age of entitlement to old-age pension in that country.

The claim will be examined by the Social Security Institute of the convention country; they check if the number years you have worked there, for which you have paid insurance contributions, is sufficient to be eligible for the pension ("qualifying period") under that country's legislation. If so – you will be entitled to an old-age pension from the convention country, and able to receive it into your bank account in Israel.

If you did not complete the minimum period of insurance required in order to be entitled to a pension ("qualifying period"), there is a possibility, provided by most conventions, to combine your years of insurance in Israel with those in the convention country. That way, you may nevertheless be entitled to a partial pension form the convention country based on "combination of insurance periods".