In Salesforce Skill Priority, the Higher priority-value skills are dropped first. Next, the Lower priority-value skills, for example 0 Priority Level value Skills are dropped last.

Sample Skills-Based Routing Rule:

Sample Apex Code to insert a Case record:

The following apex code will insert a case record so that it will include all the skills as per the Skills-Based Routing Rule setup.

insert new Case(
    Subject = 'Test',
    Priority = 'Low',
    Origin = 'Email',
    Type = 'Sales',
    Language__c = 'English',
    OwnerId = '00G4W000006YPjq'
);

Output:

Case Record is created with all the Skills. English is a required Skill. Email and Sales are additional Skills.

Sales Skill is dropped first since the Skill Priority Value is 4.

Email Skill is dropped last since the Skill Priority Value is 1.