To generate a terrain with textures in Blender using Python scripting, you can follow these steps:

### 1. Generate Terrain Mesh:

```python
import bpy

# Create terrain mesh
def create_terrain():
    bpy.ops.mesh.primitive_grid_add(x_subdivisions=100, y_subdivisions=100, size=100)
    terrain_obj = bpy.context.active_object
    terrain_obj.name = "Terrain"

create_terrain()
```

This script creates a grid mesh in Blender, which serves as the terrain.

### 2. Apply Displacement Modifier with Texture:

```python
import bpy

# Apply displacement modifier with texture
def apply_displacement_modifier():
    bpy.context.view_layer.objects.active = bpy.data.objects['Terrain']
    bpy.ops.object.modifier_add(type='DISPLACE')
    bpy.context.object.modifiers["Displace"].texture = bpy.data.textures.new("TerrainTexture", type='CLOUDS')
    bpy.context.object.modifiers["Displace"].strength = 1.0

apply_displacement_modifier()
```

This script adds a Displace modifier to the terrain object and assigns a Clouds texture to it. Adjust the texture type and strength as needed.

### 3. Apply Material and Texture:

```python
import bpy

# Apply material and texture to terrain
def apply_material_and_texture():
    terrain_obj = bpy.data.objects['Terrain']
    mat = bpy.data.materials.new(name="TerrainMaterial")
    terrain_obj.data.materials.append(mat)
    
    # Create and assign texture
    tex = bpy.data.textures.new("TerrainTexture", type='CLOUDS')
    slot = mat.texture_slots.add()
    slot.texture = tex
    slot.texture_coords = 'ORCO'  # Use object coordinates
    slot.mapping = 'FLAT'  # Apply texture flatly

apply_material_and_texture()
```

This script creates a material for the terrain and assigns a Clouds texture to it.

### 4. Export to FBX:

```python
import bpy

# Export terrain to FBX
def export_to_fbx():
    bpy.ops.export_scene.fbx(filepath="/path/to/export/terrain.fbx", use_selection=True)

export_to_fbx()
```

This script exports the terrain object to an FBX file. Replace "/path/to/export/terrain.fbx" with the desired export path.

You can run these scripts sequentially in Blender's scripting environment to generate a terrain with textures and export it to an FBX file. Once exported, you can import the FBX file into Godot and use it in your game project. Adjust the parameters and settings in the scripts to customize the terrain generation and texture application according to your requirements.