translation

my_module.my_form_configuration_tab:
  route_name: my_module.my_form_configuration
  title: Configuration
  base_route: my_module.my_form_configuration

# ...
content:
  field_copyright:
    type: text_textarea
    weight: 3
    region: content
    settings:
      rows: 2
      placeholder: ''
    third_party_settings:
      allowed_formats:
        hide_help: '1'
        hide_guidelines: '1'
      maxlength:
        maxlength_js: null
        maxlength_js_label: 'Content limited to @limit characters, remaining: <strong>@remaining</strong>'
        maxlength_js_enforce: false
# ...

$maxlength_js_label = !empty($thirdPartySettings['maxlength']['maxlength_js_label']) ? $thirdPartySettings['maxlength']['maxlength_js_label'] : t('Content limited to @limit characters, remaining: <strong>@remaining</strong>');
$maxlength_js = $thirdPartySettings['maxlength']['maxlength_js'];

# ...
content:
  field_copyright:
    type: text_textarea
    weight: 3
    region: content
    settings:
      rows: 2
      placeholder: ''
    third_party_settings:
      allowed_formats:
        hide_help: '1'
        hide_guidelines: '1'
      maxlength:
        maxlength_js: null
        maxlength_js_label: ''
        maxlength_js_enforce: false
# ...

third_party_settings:
  layout_builder:
    sections:
      1:
        layout_settings:
          label: 'My second section translation, here'
        components:
          4a5d3bb1-32d3-4a3c-a69f-6ee702a868ff:
            configuration:
              # Original: 'My first block'
              label: 'My first block that is placed in layoutbuilder translation, here'
          c1bbc85f-bb8b-4e72-9e9e-a2ccdf190646:
            configuration:
              # Original: 'My second block'
              label: 'My second block that is placed in layoutbuilder translation, here'

uuid: bedb3535-d6f2-4aae-b2cb-7f8f6e82bd5a
langcode: en
status: true
dependencies:
  config:
    - core.entity_view_mode.node.full
    - field.field.node.my_content_type.field_content
    - field.field.node.my_content_type.field_date
    - node.type.my_content_type
  module:
    - my_module
  theme:
    - my_theme
third_party_settings:
  layout_builder:
    enabled: true
    allow_custom: true
    sections:
      -
        layout_id: onecol
        layout_settings:
          label: 'My first section'
          context_mapping: {  }
        components:
          29a62ef3-00c8-40d5-8e9d-b6c3de187c10:
            uuid: 29a62ef3-00c8-40d5-8e9d-b6c3de187c10
            region: col1
            configuration:
              id: my_base_intro_block
              label: 'Intro block'
              label_display: '0'
              provider: my_base
              context_mapping:
                entity: layout_builder.entity
            weight: 0
        third_party_settings: {  }
      -
        layout_id: twocol
        layout_settings:
          label: 'My second section'
          context_mapping: {  }
        components:
          dc449aee-2be4-43d3-892e-ffd4cbe44fc0:
            uuid: dc449aee-2be4-43d3-892e-ffd4cbe44fc0
            region: col2
            configuration:
              id: 'entity_view:node'
              label: 'My first block'
              label_display: visible
              provider: ctools
              context_mapping:
                entity: layout_builder.entity
              view_mode: information
            weight: 0
          c1bbc85f-bb8b-4e72-9e9e-a2ccdf190646:
            uuid: c1bbc85f-bb8b-4e72-9e9e-a2ccdf190646
            region: col1
            configuration:
              id: 'field_block:node:my_content_type:field_content'
              label: 'My second block'
              label_display: visible
              provider: layout_builder
              context_mapping:
                entity: layout_builder.entity
                view_mode: view_mode
              formatter:
                type: text_default
                label: above
                settings: {  }
                third_party_settings: {  }
            weight: 0
        third_party_settings: {  }

// Assume $entity is your translatable entity object.
$default_language_entity = $entity->getUntranslated();
$default_language_code = $default_language_entity->language()->getId();