I am an Indian national. Right now I am staying in Israel. I will be moving to Germany on the last week of this month with german national visa directly from tel aviv. Ticket price of direct flight is high. So I am thinking to buy either Air France or LOT for travelling having layover at Paris or Poland. Am I allowed to do that? I mean is it mandatory to enter in Germany first? May I travel with these airlines with proper transit visa?
Am I allowed to do that?
Yes. A national visa from a Schengen country entitles you to visit the other Schengen countries within the 90-days-in-180 rule. Even if your visa were restricted to Germany only (which would be most exceptional), it would allow you to enter other Schengen countries for the purpose of transit to Germany.
The latter provision is found in Article 6(5)(a) of the Schengen Borders Code:
By way of derogation from paragraph 1:
(a) third-country nationals who do not fulfil all the conditions laid down in paragraph 1 but who hold a residence permit or a long-stay visa shall be authorised to enter the territory of the other Member States for transit purposes so that they may reach the territory of the Member State which issued the residence permit or the long-stay visa, unless their names are on the national list of alerts of the Member State whose external borders they are seeking to cross and the alert is accompanied by instructions to refuse entry or transit;
I mean is it mandatory to enter in Germany first?
May I travel with these airlines with proper transit visa?
You are likely to be unable to get a transit visa because as the holder of a German national visa you do not need one.