replace-strings-with-expression.js

export default function ({ types: t }) {
  return {
    visitor: {
      JSXText(path) {
	path.replaceWith(
          t.expressionStatement(
            t.callExpression(
              t.identifier('__'),
              [t.stringLiteral(path.node.value)]
            )
          )
        );
      },
      
      JSXExpressionContainer(path) {
        const binding = path.scope.bindings[path.node.expression.name];
        
        if (!t.isStringLiteral(binding.path.node.init)) {
          return;
        }
        
        binding.path.replaceWith(t.variableDeclarator(
          path.node.expression,
            t.callExpression(
              t.identifier('__'),
              [t.stringLiteral(binding.path.node.init.value)]
            )
        ));
      }
    }
  };
}

tests.js

class I18N extends React.Component {
  render() {
    return (
      <div>'Hello World'</div>
    );
  }
}

class Variable extends React.Component {
  render() {
    const string = `Some ${1 + 1}`;
    
    return <div>{string}</div>;
  }
}