The majority of customers affected have already been re-accommodated on another Ryanair flight.
At a Frankfurt press conference on Wednesday, Ryanair's chief marketing officer Kenny Jacobs said the company's German pilots enjoy "excellent working conditions".
Ryanair, which flies in 37 countries and carried 130 million passengers last year, averted widespread Christmas strikes last year by agreeing to recognise trade unions for the first time in its 33-year history.
A Dutch court rejected a case from Ryanair seeking to block pilots in the Netherlands from joining Friday's strike, but the Irish airline said all of its flights there would run as scheduled.
"The only reason I found this out was through a reminder email about checking in being sent to my email account".More news: Australia's most populous state is now entirely in drought
In Belgium, Ryanair has cancelled 20 flights: eight between Zaventem airport and Madrid and Barcelona, and 12 between Charleroi and Alicante, Almería, Santander, Seville, Tenerife and Zaragoza.
"They couldn't find us any alternative flights until Sunday".
She tried to find any other flights to Sweden from other United Kingdom airports, and even asked if she could fly to Copenhagen in Denmark, and get a train to Gothenburg instead.
Ryanair operates more than 2,000 flights a day, serving 223 airports across 37 countries in Europe and North Africa, and insists it will not change the low-priced model that transformed the industry and has made it Europe's most profitable airline.
Ryanair planes have a capacity of 189, meaning more than 74,000 passengers could be affected.More news: Canada shooting: Several dead in Fredericton, New Brunswick
Ryanair called the demands "pointless", and posted details of how much the cabin crew earn and said they receive an annual uniform allowance of €400.
In Sweden, around 40 Ryanair pilots were striking until midnight between Friday and Saturday.
Ryanair has slammed the strikes as "unnecessary" but pilots counter that the carrier has refused to engage in meaningful dialogue about collective labour agreements since it began recognising unions in December 2017.
Ryanair released a statement which reads: "We took every step to minimise the disruption and we notified our customers as early as possible advising them of their free move, refund or reroute options".
The airline has maintained that strikes qualify as "extraordinary circumstances" and are therefore exempt from European Union compensation rules.More news: Mourinho doesn't envisage Yerry Mina at Manchester United
Consumer group Which? said affected passengers should lodge a claim with the airline. "The strike may go ahead", judge Theo Roell said.