/**
 * @name mnemonicToLegacySeed
 * @summary Creates a valid Ethereum/Bitcoin-compatible seed from a mnemonic input
 * @example
 * <BR>
 *
 * ```javascript
 * import { mnemonicGenerate, mnemonicToLegacySeed, mnemonicValidate } from '@polkadot/util-crypto';
 *
 * const mnemonic = mnemonicGenerate(); // => string
 * const isValidMnemonic = mnemonicValidate(mnemonic); // => boolean
 *
 * if (isValidMnemonic) {
 *   console.log(`Seed generated from mnemonic: ${mnemonicToLegacySeed(mnemonic)}`); => u8a
 * }
 * ```
 */
export declare function mnemonicToLegacySeed(mnemonic: string, password?: string, onlyJs?: boolean, byteLength?: 32 | 64): Uint8Array;