Wikipedia has guides for it; Check the downloading wikipedia section. The most popular offline client atm is Kiwix reader

Kiwix is the easiest way to do it; if you have Docker/Kubernetes, there's a Docker image at ghcr.io/kiwix/kiwix-serve, and the K8s manifest to deploy is as simple as:

apiVersion: v1
kind: Service
metadata:
  name: wikipedia-service
spec:
  selector:
    app: kiwix-server
  ports:
  - port: 80
    targetPort: 8080
  clusterIP: None
***
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wikipedia-server
  labels:
    app: kiwix-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: kiwix-server
  template:
    metadata:
      name: wikipedia-server
      labels:
        app: kiwix-server
    spec:
      containers:
      - name: kiwix-server
        image: kiwix/kiwix-serve:3.8.0
        imagePullPolicy: IfNotPresent
        command:
        - /usr/local/bin/kiwix-serve
        - --port=8080
        - --verbose
        - /data/wikipedia_en_all_maxi.zim
        ports:
        - containerPort: 8080
          protocol: TCP
        volumeMounts:
        - name: data
          mountPath: /data
          readOnly: true
          limits:
            memory: "128Mi"
            cpu: "2000m"
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: wikipedia-mirror

Then you just need to download a copy of the mirror file wikipedia_en_all_maxi.zim and put it in the appropriate place - wget https://download.kiwix.org/zim/wikipedia_en_all_maxi.zim